title: Unable to start rails server with an gem error?
body: <p>After I type rails s in terminal, I got this error:</p>
  
  <blockquote>
    <p>/Users/freefrog/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/railties-4.2.4/lib/rails/railtie.rb:196:in <code>method_missing': undefined local variable or method</code>mongoid' for Raceday::Application:Class (NameError)
    Did you mean?  mongoize</p>
  </blockquote>
  
  <p>what's that mean? It looks like something is wrong with gem file? but bundle show that everything goes well.</p>