Summary:
* Reduces size of final image from 5GB to 130MB
* Builds any checkout (not locked to the master)
* Doesn't run stack on CMD (executes static build of Duckling instead)
Pull Request resolved: https://github.com/facebook/duckling/pull/341
Reviewed By: chinmay87
Differential Revision: D21083018
Pulled By: patapizza
fbshipit-source-id: d909158f20f5b8da5b0248a25103b850797bc3a3