Update mocha version to 0.13.0 and change requires
Remove not used variable warning
Fix indentation to remove warning
remove the warning when testing whiny_nil
Fix build. It seems that the Mocha's behavior were changed.
Update failing tests overriding destroy method instead of using mocha expectation

Mocha by default does not allow adding expectation to frozen objects,
just applying a workaround to ensure the method is never called, making
the tests pass without enabling this again in mocha.
Remove obsolete rake/rdoctask require

Requiring this now raises a RuntimeError, failing the test.
It also seems that the require is unnecessary to pass the test.