Change dependency to correct Hamcrest GitHub repo.

Together with @cordoval and @davedevelopment we've updated @cordoval version of Hamcrest-php library on GitHub (to 1.1.0) and published it on Composer as well.

Then fork of @davedevelopment (based on 1.0.0) would be deleted and your tests would break. To prevent that I've changed a dependency to correct Composer package.

I've also made tests use Hamcrest from Composer, rather one from PEAR. I've checked, that  all tests pass (some were skipped) after the changes.