Rename testing.Fake to testing.Stub.

[ericsnowcurrently]

Gustavo pointed out that "Fake" probably isn't the right name for this kind of testing double.
Although nomenclature for testing doubles is inconsistent, I'll follow the definitions from Meszaros's xUnit book [1] as summarized by Fowler [2]:

fake: has working (but not production suitable) implementation
stub: provides canned answers and records info about calls
mock: pre-programmed with expectations about expected calls

[1] http://xunitpatterns.com/Mocks,%20Fakes,%20Stubs%20and%20Dummies.html
[2] http://martinfowler.com/articles/mocksArentStubs.html#TheDifferenceBetweenMocksAndStubs

[natefinch]

LGTM