Log Message:
Update ruby-bcrypt to 3.1.7.

3.1.3  Feb 21 2014
  - Add support for Ruby 2.1 in compiled Windows binaries
  - Rename gem from "bcrypt-ruby" to just "bcrypt". [GH #86 \ 
by @sferik]

3.1.6  Feb 21 2014
  - Dummy version of "bcrypt-ruby" needed a couple version bumps to \ 
fix some
    bugs. It felt wrong to have that at a higher version than the real gem, so
    the real gem is getting bumped to 3.1.6.

3.1.7  Feb 24 2014
  - Rebuild corrupt Java binary version of gem [GH #90]
  - The 2.1 support for Windows binaries alleged in 3.1.3 was a lie -- \ 
documentation removed