Fixed the spec for callable argument support

My previous PR broke the specs as I missed some places where method calls had to be allowed to avoid being considered as an unexpected calls.

As I'm now able to run the full spec locally thanks to https://github.com/phpspec/phpspec/pull/148, I was able to figure it even if Travis is failing.

I'm also fixing the travis installation until composer fixes the guessing of the root version for the newest git versions. Otherwise, the installation will always fail as phpspec/phpspec depends on prophecy 1.x.