Change version requirement for rspec to not be so open ended
Fix travis config to use more recent version of rubygems

* There appears to be a bug in how the dependencies are resolved for
  jruby in 1.8 mode. It is likely either the ruby version or an old
  version of bundler. Given that the rubygems version on travis is
  so far out-of-date I'm going to attempt this first and follow up
  with a bundler upgrade should it fail.