em-websocket has been installed, but wrong with "cannot load such file -- em-websocket(LoadError)"

[collinsyu]

ruby version 2.0.0p648 ; bundler version 1.15.3 ;

wrong message: /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:inrequire': cannot load such file -- em-websocket (LoadError) from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in require' from em/daemon.rb:8:in

' ` how actually run the project?