Remove keyword args to be compatible ruby 1.9 series

The current implementation only uses keyword args at one point, so ruby 2.0
is not really needed.

Also, a lot of projects still uses ruby 1.9, so the loaded ruby will be the
1.9 (to run tests, app etc).

So I think that is a good idea to support the 1.9 series.

PS: This gem rocks! Thank you :sparkles: