Merge pull request #1 from borisyankov/master

Merging upstream changes
mock `expects` should return an `Expectation`, rather than a `ExpectationStatic`.

http://sinonjs.org/docs/#mocks
Merge pull request #417 from richardTowers/sinon-mock

Sinon mock's should return `SinonExpectation`s, not `SinonExpectationStatic`s