Update src21/src21railsexpress to MRI 2.1.5, Rubygems 2.4.4, and Bundler 1.7.6

Tested and working on an existing production server. Railsexpress patches have also been updated with the latest from https://github.com/skaes/rvm-patchsets/tree/master/patches/ruby/2.1.5/railsexpress