Bump to 2.0.x for requirement of ruby 1.9.3 or higher.

Continuing to support 1.8.7 is difficult when gems don't list their
incompatibilities with old rubies. Hunting for versions that work
just isn't a good use of time when rails and more have moved to 1.9.3
and above.
Report version information to help make ruby version jumps easier in the future