Merge branch 'stable-3.1'
* stable-3.1:
Documentation: Fix parentForDeletedProjects in config.md
Adapt the change in Gerrit core
Bump Bazel version to 2.2.0
Bump required Bazel version to 2.1.0
Upgrade bazlets to latest stable-2.16 to build with 2.16.16 API
Documentation: Refactor to match other plugin documentation
Add an empty tools/BUILD file explicitly for Bazel
Upgrade bazlets to latest stable-2.16
Upgrade bazlets to latest stable-2.16
Upgrade bazlets to latest stable-2.15
Upgrade bazlets to latest stable-2.14
config.md: Correct formatting of config values
Change-Id: Ib51ef5f829d0b318cffc41c44f83eb56e55a53df