Merge branch 'stable-3.1'

* stable-3.1:
  Update bazlets to latest stable-3.1 to build with 3.1.4 API
  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: I6c2bb4a7a4df688329c1448ff31703e592b6759e

.bazelversion

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