title: Rails4 + devise + mongoid - `require': cannot load such file -- mongoid/version (LoadError)
body: <p>I am trying to use rails4 with mongoid and devise. I have this in my Gemfile</p>
  
  <pre><code>gem 'rails', '4.0.0'
  gem 'mongoid'
  gem 'devise'
  </code></pre>
  
  <p><code>bundle install</code> is successfull. But when i try to start <code>rails server</code>, I get this error</p>
  
  <pre><code>Exiting
  /home/username/.rvm/gems/ruby-2.0.0-p0/gems/activesupport-4.0.0/lib/active_support/dependencies.rb:228:in `require': cannot load such file -- mongoid/version (LoadError)
      from /home/username/.rvm/gems/ruby-2.0.0-p0/gems/activesupport-4.0.0/lib/active_support/dependencies.rb:228:in `block in require'
      from /home/username/.rvm/gems/ruby-2.0.0-p0/gems/activesupport-4.0.0/lib/active_support/dependencies.rb:213:in `load_dependency'
      from /home/username/.rvm/gems/ruby-2.0.0-p0/gems/activesupport-4.0.0/lib/active_support/dependencies.rb:228:in `require'
      from /home/username/.rvm/gems/ruby-2.0.0-p0/gems/devise-3.0.0/lib/devise/rails.rb:34:in `block in &lt;class:Engine&gt;'
      from /home/username/.rvm/gems/ruby-2.0.0-p0/gems/railties-4.0.0/lib/rails/initializable.rb:30:in `instance_exec'
      from /home/username/.rvm/gems/ruby-2.0.0-p0/gems/railties-4.0.0/lib/rails/initializable.rb:30:in `run'
      from /home/username/.rvm/gems/ruby-2.0.0-p0/gems/railties-4.0.0/lib/rails/initializable.rb:55:in `block in run_initializers'
  </code></pre>
  
  <p>I am using Ruby 2.0.0 on Ubuntu</p>