Exclude the duplicated Ruby v2.1.0 run

We only run coverage on 2.1.0 but due to the testing matrix we actually
run the same tests twice.

Hopefully this removes the run without coverage.
Remove testing for 1.9.2

Never seen any differences/issues between 1.9.2 and 1.9.3 and I guess it
isn't the most used version.

This way we free up a Travis box for someone else.
Exclude the duplicated Ruby v2.1.0 run (v2)

We only run coverage on 2.1.0 but due to the testing matrix we actually
run the same tests twice.

Hopefully this removes the run without coverage (since the last one was
the wrong version).
simplify travis.yml to just use explicit includes
Merge pull request #2672 from fog/reduce_ci_burden

Reduce Travis CI burden