Remove support for RBX.

It's no longer supported on TravisCI, no one uses it anyways.
While we're at it, why not add some new rubies?
Add some rbx love back in.

Because some people use it and it's not that difficult.
Merge branch 'pr-travis_error' of https://github.com/IoraHealth/ruby-hl7 into IoraHealth-pr-travis_error

Conflicts:
	.travis.yml
Merge branch 'IoraHealth-pr-travis_error'