我最近安装并创建了一个新项目，我遵循了 Rails 教程（http://guides.rubyonrails.org/getting_started.html），一切正常。
现在，当我尝试创建一个新项目并启动服务器时，我得到了这个：
=> Booting WEBrick
=> Rails 4.0.0 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
[2013-09-09 15:28:55] INFO WEBrick 1.3.1
[2013-09-09 15:28:55] INFO ruby 2.0.0 (2013-06-27) [x64-mingw32]
[2013-09-09 15:28:55] INFO WEBrick::HTTPServer#start: pid=12064 port=3000
Started GET "/" for 127.0.0.1 at 2013-09-09 15:28:56 +0100
Gem::LoadError (Specified 'sqlite3' for database adapter, but the gem is not loa
ded. Add `gem 'sqlite3'` to your Gemfile.):
activerecord (4.0.0) lib/active_record/connection_adapters/connection_specific
ation.rb:58:in `rescue in resolve_hash_connection'
activerecord (4.0.0) lib/active_record/connection_adapters/connection_specific
ation.rb:55:in `resolve_hash_connection'
activerecord (4.0.0) lib/active_record/connection_adapters/connection_specific
ation.rb:46:in `resolve_string_connection'
activerecord (4.0.0) lib/active_record/connection_adapters/connection_specific
ation.rb:30:in `spec'
activerecord (4.0.0) lib/active_record/connection_handling.rb:39:in `establish
_connection'
activerecord (4.0.0) lib/active_record/railtie.rb:175:in `block (2 levels) in
<class:Railtie>'
activesupport (4.0.0) lib/active_support/lazy_load_hooks.rb:38:in `instance_ev
al'
activesupport (4.0.0) lib/active_support/lazy_load_hooks.rb:38:in `execute_hoo
k'
activesupport (4.0.0) lib/active_support/lazy_load_hooks.rb:45:in `block in ru
n_load_hooks'
activesupport (4.0.0) lib/active_support/lazy_load_hooks.rb:44:in `each'
activesupport (4.0.0) lib/active_support/lazy_load_hooks.rb:44:in `run_load_ho
oks'
activerecord (4.0.0) lib/active_record/base.rb:322:in `<module:ActiveRecord>'
activerecord (4.0.0) lib/active_record/base.rb:22:in `<top (required)>'
activerecord (4.0.0) lib/active_record/query_cache.rb:50:in `restore_query_cac
he_settings'
activerecord (4.0.0) lib/active_record/query_cache.rb:43:in `rescue in call'
activerecord (4.0.0) lib/active_record/query_cache.rb:32:in `call'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection
_pool.rb:626:in `call'
activerecord (4.0.0) lib/active_record/migration.rb:369:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:29:in `block in
call'
activesupport (4.0.0) lib/active_support/callbacks.rb:373:in `_run__342058401_
_call__callbacks'
activesupport (4.0.0) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/reloader.rb:64:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `c
all'
actionpack (4.0.0) lib/action_dispatch/middleware/show_exceptions.rb:30:in `ca
ll'
railties (4.0.0) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.0.0) lib/rails/rack/logger.rb:21:in `block in call'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `block in tag
ged'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:25:in `tagged'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `tagged'
railties (4.0.0) lib/rails/rack/logger.rb:21:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.2) lib/rack/runtime.rb:17:in `call'
activesupport (4.0.0) lib/active_support/cache/strategy/local_cache.rb:83:in `
call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/static.rb:64:in `call'
railties (4.0.0) lib/rails/engine.rb:511:in `call'
railties (4.0.0) lib/rails/application.rb:97:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
rack (1.5.2) lib/rack/content_length.rb:14:in `call'
rack (1.5.2) lib/rack/handler/webrick.rb:60:in `service'
C:/Ruby200-x64/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service'
C:/Ruby200-x64/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run'
C:/Ruby200-x64/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'
Rendered C:/Ruby200-x64/lib/ruby/gems/2.0.0/gems/actionpack-4.0.0/lib/action_d
ispatch/middleware/templates/rescues/_source.erb (2.0ms)
Rendered C:/Ruby200-x64/lib/ruby/gems/2.0.0/gems/actionpack-4.0.0/lib/action_d
ispatch/middleware/templates/rescues/_trace.erb (2.0ms)
Rendered C:/Ruby200-x64/lib/ruby/gems/2.0.0/gems/actionpack-4.0.0/lib/action_d
ispatch/middleware/templates/rescues/_request_and_response.erb (2.0ms)
Rendered C:/Ruby200-x64/lib/ruby/gems/2.0.0/gems/actionpack-4.0.0/lib/action_d
ispatch/middleware/templates/rescues/diagnostics.erb within rescues/layout (122.
1ms)
当我打开浏览器窗口时，我得到
Gem::LoadError 为数据库适配器指定了“sqlite3”，但 gem 没有加载。添加gem 'sqlite3'到您的 Gemfile。
我能做些什么来解决这个问题？