(PUP-3479) Update ffi version to 1.9.5

ffi-1.9.5 is required by Ruby 2.1.x. The Gemfile has been updated on
 puppet. Replace ffi-1.9.3 with ffi-1.9.5.
Merge pull request #67 from MikaelSmith/task/2.0.0-x64/PUP-3479-update-ffi

(PUP-3479) Update ffi version to 1.9.5 (2.0.0-x64)