Revert "[split] Revert "upload the scrooge sbt plugin to bintray""

Looks like this got reverted because of a failed travis build https://travis-ci.org/twitter/scrooge/builds/23263652

I think travis failed for a different reason (and we are fixing that). Reverting the revert to bring back sbt plugin publishing.

This reverts commit bd463d9a581bdce48c37754b866c4bbd04b8fb21.