Merge branch 'stable-3.1'

* stable-3.1:
  Upgrade bazlets to latest stable-2.16 to build with 2.16.18 API
  Bump Bazel version to 3.1.0

Change-Id: Ifb0d352a07de8c71797573f8262204aca0e7b428
tree: 69c6750d35efcde2856f6fc282ed08c54b1197c8
  1. src/
  2. BUILD
  3. LICENSE