add es3-safe-transpile step

currently just:

`promise.finally` -> `promise[‘finally’]`
`promise.catch`  -> `promise[‘catch’]`
`a.default`  -> `a[‘default’]`

and the object literal versions

The transpile step stuff support source maps but the rest of our pipeline doesn't quite yet.

related:
https://github.com/stefanpenner/es3-safe-recast/ 
https://github.com/stefanpenner/broccoli-es3-safe-recast/