Remove jruby and 1.9.3 from build matrix

The `mutant` gem specifies Ruby >= 2.0.0:

https://github.com/mbj/mutant/blob/75164ba31a9129fc16d27d7f4a3e741a90da4a12/mutant.gemspec#L24
Merge pull request #24 from moneyadviceservice/remove-ruby-1-9-from-travis

Remove jruby and 1.9.3 from build matrix