Updating submodules
Updating submodules

Summary:
GitHub commits:

https://github.com/facebook/proxygen/commit/6c1522e6b47e1c463d09ab6665f1af8f1a9f51e6
https://github.com/facebookexternal/stl_tasks/commit/4cadf79848467886c995e140efb0e19dc26c75b3
https://github.com/facebookincubator/velox/commit/ecd8333681528fbc94365e35c8106eb950ab2ee7

Reviewed By: bigfootjon

fbshipit-source-id: 244813db1e197b1275f3314b7bb7d07ede66778b

facebook/bistro,facebook/bistro,facebook/bistro,facebook/bistro,facebook/bistro,facebook/bistro