当我尝试启动“padrino sample_blog”时遇到了这个错误。我安装了 'multi_json' 和 'atomic' gems 的更新版本，但我无法启动博客并且不知道如何解决它，有什么帮助吗？
:sample_blog user$ padrino start
警告：Gem::Specification.reset 期间未解决的规范：
multi_json (~> 1.3)
atomic (>= 0)
警告：清除未解决的规范。如果这会导致问题，请报告错误。
/usr/local/rvm/gems/ruby-1.9.3-p392/gems/padrino-core-0.9.21/lib/padrino-core/cli/base.rb:1:in `require': 无法加载这样的文件-- 雷神 (LoadError)
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/padrino-core-0.9.21/lib/padrino-core/cli/base.rb:1:in `<top (required)>'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/padrino-core-0.9.21/bin/padrino:7:in `require'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/padrino-core-0.9.21/bin/padrino:7:in `<top (required)>'
from /usr/local/rvm/gems/ruby-1.9.3-p392/bin/padrino:23:in `load'
from /usr/local/rvm/gems/ruby-1.9.3-p392/bin/padrino:23:in `<main>'
from /usr/local/rvm/gems/ruby-1.9.3-p392/bin/ruby_noexec_wrapper:14:in `eval'
from /usr/local/rvm/gems/ruby-1.9.3-p392/bin/ruby_noexec_wrapper:14:in `<main>'