Update ruby-flexmock to 2.2.1.

2.2.0:

- #new_instances now mocks the #initialize method instead of mocking after the
  allocation was done. This allows to do mock methods called by #initialize
  itself. Behaviour when the allocator is explicitely provided is left
  unchanged, which means that the old behaviour is still available by passing
  :new to new_instances.

2.1.0:

- added `#and_iterates` to fix some shortcomings of `#and_yield` without
  breaking backward compatibility
- strict partial mocks (and "based mocks" if `FlexMock.partials_are_based` is
  set to true) are now based on the object's singleton class, instead of its
  class.

(taca)