Have OSS getdeps.py pull code from 'main' (instead of 'master') until all repos are migrated
Have OSS getdeps.py pull code from 'main' (instead of 'master') until all repos are migrated

Summary: getdeps.py pulls repos from master branch by default. For FBOSS force it to pull from 'main'

Reviewed By: shri-khare

Differential Revision: D30857755

fbshipit-source-id: 9891f1ddc08c8f13bdcb00385e1ad4516a84776c

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly