update for ruby2

Hi!

Thanks for the Gem.

I wanted to update this gem to work with ruby2, as all of the FasterCSV => CSV checks just checked if the ruby version was 1.9

there is a failing encoding test, in the specs, and your caller may need to call force_encoding('UTF-8') before saving the result in a ruby2 env, so I was hoping to possibly get some feedback to make this work, or at least have a pull request for people who may want to try this novel approach to a very annoying problem on Ruby 2.0.


Any help is much appreciated!