(maint) run the tests under travis again

NOTE: This probably isn't safe to merge yet, as it uncovers a bunch of failing examples that had been allowed to slide by.

rcov and ext/packaging/packaging.rake are failing to load, but that means it's
also failing to load the rspec and rspec/core/rake_task so the command we use
to test the gem is silently succeeding all the time rather than actually
running the spec tests.