Log Message:
Update ruby-rspec-mocks to 3.2.1.

### 3.2.1 / 2015-02-23
[Full Changelog](http://github.com/rspec/rspec-mocks/compare/v3.2.0...v3.2.1)

Bug Fixes:

* Add missing `rspec/support/differ` require so that rspec-mocks can be
  used w/o rspec-expectations (which also loads the differ and hided the
  fact we forgot to require it). (Myron Marston, #893)
* Revert tracking of received arg mutation (added in 3.2.0 to provide an
  error in a situation we can't support) as our implementation has side
  effects on non-standard objects and there's no solution we could come
  up with that always works. (Myron Marston, #900)