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
  Bump Bazel version to 3.0.0

Change-Id: Ie7e25c6d18f4bd0e98f8c65e416fb777688401b3
diff --git a/.bazelversion b/.bazelversion
index ccbccc3..fd2a018 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.2.0
+3.1.0