version to 2.12.2

* Handle stubbing a method on a parent and child in the same test (#199)
* Basic stub system tests, instance and singleton methods (#200)
* Add readable inspect to `Stub` (#201)
* Stub system tests for mixed in and inherited methods (#202)
* Stub system tests for delegated methods (#203)
* Better arity error messages (#206)
* Store stub ivars on `Assert` not on the object being stubbed (#205)
* Match arity when defining proxy method with stubbing (#204)

/cc @kellyredding