title: Bundler error with passenger-install-nginx-module on ubuntu 14.04
body: <p>I am installing passenger + nginx on <code>ubuntu 14.04</code> &amp; <code>ruby 2.2.4</code>. There are <code>bundler</code> errors with <code>passenger-install-nginx-module</code>   </p>
  
  <pre><code>  $passenger-install-nginx-module
      /home/ubuntu/.rvm/gems/ruby-2.2.4/gems/bundler-1.13.1/lib/bundler/rubygems_ext.rb:45:in `full_gem_path': uninitialized constant Bundler::Plugin::API::Source (NameError)
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/basic_specification.rb:144:in `block in full_require_paths'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/basic_specification.rb:143:in `map'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/basic_specification.rb:143:in `full_require_paths'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/basic_specification.rb:76:in `contains_requirable_file?'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/specification.rb:949:in `block in find_in_unresolved'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/specification.rb:949:in `each'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/specification.rb:949:in `find_all'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/specification.rb:949:in `find_in_unresolved'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:74:in `require'
              from /home/ubuntu/.rvm/gems/ruby-2.2.4/gems/bundler-1.13.1/lib/bundler/plugin/api/source.rb:2:in `&lt;top (required)&gt;'
              from /home/ubuntu/.rvm/gems/ruby-2.2.4/gems/bundler-1.13.1/lib/bundler/rubygems_ext.rb:45:in `full_gem_path'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/basic_specification.rb:144:in `block in full_require_paths'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/basic_specification.rb:143:in `map'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/basic_specification.rb:143:in `full_require_paths'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/specification.rb:1370:in `add_self_to_load_path'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/specification.rb:1283:in `activate'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_gem.rb:67:in `block in gem'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_gem.rb:66:in `synchronize'
              from /home/ubuntu/.rvm/rubies/ruby-2.2.4/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_gem.rb:66:in `gem'
              from /home/ubuntu/.rvm/gems/ruby-2.2.4/bin/passenger-install-nginx-module:22:in `&lt;main&gt;'
              from /home/ubuntu/.rvm/gems/ruby-2.2.4/bin/ruby_executable_hooks:15:in `eval'
              from /home/ubuntu/.rvm/gems/ruby-2.2.4/bin/ruby_executable_hooks:15:in `&lt;main&gt;'
  </code></pre>
  
  <p>Before that, <code>gem passenger (v5.0.30)</code> and <code>rails 4.2.0</code> have been installed. What causes the error? </p>