railsapps - "$ rails s" gives following error

Question

/Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_require.rb:54:in require': cannot load such file -- rubygems/format (LoadError) from /Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_require.rb:54:inrequire' from /Users/jay/.rvm/gems/ruby-2.1.2/gems/bundler-1.0.22/lib/bundler/source.rb:5:in <top (required)>' from /Users/jay/.rvm/gems/ruby-2.1.2/gems/bundler-1.0.22/lib/bundler/dsl.rb:14:ininitialize' from /Users/jay/.rvm/gems/ruby-2.1.2/gems/bundler-1.0.22/lib/bundler/dsl.rb:6:in new' from /Users/jay/.rvm/gems/ruby-2.1.2/gems/bundler-1.0.22/lib/bundler/dsl.rb:6:inevaluate' from /Users/jay/.rvm/gems/ruby-2.1.2/gems/bundler-1.0.22/lib/bundler/definition.rb:17:in build' from /Users/jay/.rvm/gems/ruby-2.1.2/gems/bundler-1.0.22/lib/bundler.rb:138:indefinition' from /Users/jay/.rvm/gems/ruby-2.1.2/gems/bundler-1.0.22/lib/bundler.rb:126:in load' from /Users/jay/.rvm/gems/ruby-2.1.2/gems/bundler-1.0.22/lib/bundler.rb:110:insetup' from /Users/jay/project_mon/config/boot.rb:8:in <top (required)>' from /Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_require.rb:54:inrequire' from /Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_require.rb:54:in require' from script/rails:5:in'