Modify Ruby versions for Travis
Modify Ruby versions for Travis

Change the .travis.yml file so that Travis no longer runs
the tests against Ruby 1.8.7 and 1.9.2 since the Endian
modifiers were not added to Array#pack until 1.9.3.  While
we're add it add Ruby 2.0.0 and 2.1.0 to the file to run
the tests against the newer Rubies.

ManageIQ/binary_struct