Add support for ES6 classes in sort-comp

[lencioni]

In a comment in sort-comp, I noticed the following comment:

NOTE: only works on React.createClass() syntax, not ES6 class.

It would be really lovely if this worked with ES6 classes. 😺

[cpojer]

we are not taking support requests for this repository. We'll publish React codemods that we build at Facebook and are happy to take pull requests – feel free to dabble into the code and send us one ;)