Use latest Travis::Logger API from travis-support
Add Celluloid mocking workaround

This workaround is taken from celluloid/celluloid#26 and is needed to avoid
infinite loops when using mocking and Celluloid.
Use a StandardError in the specs instead of Exception

We no longer capture Exception, but StandardError instead.

Also added a text so that it's easier to find this exception if the specs failed
and the exception get raised to the top level (previously it would just complain
about an exception "Exception" being raised with no other information).
Remove trailing whitespace