Replace the formatter in the rspec SPEC_OPTS

TravisCI does not seem to enable the 'n' formatter anymore, hence
we use the documentation one.
Force travis/spec to use RSPEC version 2.14.x

Since our test are not rspec 3.0.0 ready, we need to force travis
to use rspec version 2.14.x
Merge pull request #485 from enovance/change_rspec_formatter

Replace the formatter in the rspec SPEC_OPTS