added 2.0.0 and 2.1.0 versions to travis file
Added Ruby 2.0.0 and 2.1.0 versions to travis file.
Merge branch '2_0_x' of github.com:nkts/redis_failover into 2_0_x
Merge pull request #76 from nkts/2_0_x

Run tests with Ruby 2.0.0 and 2.1.0