Update babel versions

[BookOfGreg]

Adds modern rubies, modern babel, removes some older versions to speed travis.

[BookOfGreg]

@loganfsmyth
As discussed in this thread:
babel/babel#8893
And also in the originating react-rails thread of which I am a member:
reactjs/react-rails#944
I've started basic work to get this gem running again.

The Travis CI won't pass until I have released new babel-source versions which this gem also contains.
https://rubygems.org/gems/babel-source/versions/4.7.16
I also see that @tricknotes had a repository for babel-6 support that I might adopt.
https://github.com/tricknotes/ruby-babel-transpiler/tree/babel-source-6

Would any of the people I mentioned be able to either grant me access to release these gems or release on my behalf?
Thanks.