fbcode_builder: getdeps: add Python3.7.6 manifest
fbcode_builder: getdeps: add Python3.7.6 manifest

Summary:
As titled.

FBOSS depends on Python3.7.6, subsequent diff in the stack adds Python3.7.6
depedency for FBOSS.

Differential Revision: D20064316

fbshipit-source-id: 27b328dc25e326f3927ea6cb003fb7bb45732d61

facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman