Rails 服务器在启动时一直退出。自从升级到 4 后，我遇到了许多错误，并且我一直在一次修改一个。这是我似乎无法弄清楚的一个。起初它不会因为 *.rb 文件中的错误而启动，现在它什么也没说。请帮忙？
=> Booting WEBrick
=> Rails 4.0.1 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Exiting
/usr/local/rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.1/lib/active_record/connection_adapters/connection_specification.rb:58:in `rescue in resolve_hash_connection': Specified 'sqlite3' for database adapter, but the gem is not loaded. Add `gem 'sqlite3'` to your Gemfile. (Gem::LoadError)
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.1/lib/active_record/connection_adapters/connection_specification.rb:55:in `resolve_hash_connection'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.1/lib/active_record/connection_adapters/connection_specification.rb:46:in `resolve_string_connection'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.1/lib/active_record/connection_adapters/connection_specification.rb:30:in `spec'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.1/lib/active_record/connection_handling.rb:39:in `establish_connection'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.1/lib/active_record/railtie.rb:176:in `block (2 levels) in <class:Railtie>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/lazy_load_hooks.rb:38:in `instance_eval'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/lazy_load_hooks.rb:38:in `execute_hook'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/lazy_load_hooks.rb:45:in `block in run_load_hooks'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/lazy_load_hooks.rb:44:in `each'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/lazy_load_hooks.rb:44:in `run_load_hooks'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.1/lib/active_record/base.rb:322:in `<module:ActiveRecord>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.1/lib/active_record/base.rb:22:in `<top (required)>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise/orm/active_record.rb:3:in `<top (required)>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:229:in `require'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:229:in `block in require'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:214:in `load_dependency'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:229:in `require'
from /Users/andresalaz/Desktop/code/andre/config/initializers/devise.rb:22:in `block in <top (required)>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise.rb:276:in `setup'
from /Users/andresalaz/Desktop/code/andre/config/initializers/devise.rb:3:in `<top (required)>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:223:in `load'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:223:in `block in load'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:214:in `load_dependency'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:223:in `load'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/engine.rb:609:in `block (2 levels) in <class:Engine>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/engine.rb:608:in `each'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/engine.rb:608:in `block in <class:Engine>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/initializable.rb:30:in `instance_exec'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/initializable.rb:30:in `run'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/initializable.rb:55:in `block in run_initializers'
from /usr/local/rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:150:in `block in tsort_each'
from /usr/local/rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:183:in `block (2 levels) in each_strongly_connected_component'
from /usr/local/rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:210:in `block (2 levels) in each_strongly_connected_component_from'
from /usr/local/rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:219:in `each_strongly_connected_component_from'
from /usr/local/rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:209:in `block in each_strongly_connected_component_from'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/initializable.rb:44:in `each'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/initializable.rb:44:in `tsort_each_child'
from /usr/local/rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:203:in `each_strongly_connected_component_from'
from /usr/local/rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:182:in `block in each_strongly_connected_component'
from /usr/local/rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:180:in `each'
from /usr/local/rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:180:in `each_strongly_connected_component'
from /usr/local/rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:148:in `tsort_each'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/initializable.rb:54:in `run_initializers'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/application.rb:215:in `initialize!'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/railtie/configurable.rb:30:in `method_missing'
from /Users/andresalaz/Desktop/code/andre/config/environment.rb:5:in `<top (required)>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:229:in `require'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:229:in `block in require'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:214:in `load_dependency'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.1/lib/active_support/dependencies.rb:229:in `require'
from /Users/andresalaz/Desktop/code/andre/config.ru:3:in `block in <main>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/rack-1.5.2/lib/rack/builder.rb:55:in `instance_eval'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/rack-1.5.2/lib/rack/builder.rb:55:in `initialize'
from /Users/andresalaz/Desktop/code/andre/config.ru:in `new'
from /Users/andresalaz/Desktop/code/andre/config.ru:in `<main>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/rack-1.5.2/lib/rack/builder.rb:49:in `eval'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/rack-1.5.2/lib/rack/builder.rb:49:in `new_from_string'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/rack-1.5.2/lib/rack/builder.rb:40:in `parse_file'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/rack-1.5.2/lib/rack/server.rb:277:in `build_app_and_options_from_config'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/rack-1.5.2/lib/rack/server.rb:199:in `app'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/commands/server.rb:48:in `app'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/rack-1.5.2/lib/rack/server.rb:314:in `wrapped_app'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/commands/server.rb:75:in `start'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/commands.rb:76:in `block in <top (required)>'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/commands.rb:71:in `tap'
from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.1/lib/rails/commands.rb:71:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'