Support for default params with JSXTransformer's `harmony` flag.

[appsforartists]

The following code is not transformed by JSX:

  render: function (optionalArg = "default value") {

See for yourself here.

Other transpilers, like 6to5, support this transformation.

[zpao]

Since we still use jstransform we'll get this when it does. For now I'm going to close this since there's nothing actionable to do here but wait. Thanks for filing and for filing in jstransform :)

[appsforartists]

No worries. It took me longer than it should have to find jstranform - otherwise I would have started there. ;-)