Lock minitest-reporters dependency to fix the build

On 2013-11-23, minitest-reporters released v1.0.0, which instead of
relying on minitest <= 5.0, requires minitest >= 5.0. This change breaks
the travis build since we rely on some deprecated APIs.

This change locks us to the 0.14 series of minitest-reporters.
Merge pull request #113 from yaauie/fix-minitest-dependency

Lock minitest-reporters dependency to fix the build