Merge branch 'stable-3.1'

* stable-3.1:
  Bump Bazel version to 2.2.0

Change-Id: I077fb35f38baf734e374d891ad6adce650ea138b
diff --git a/.bazelversion b/.bazelversion
index 7ec1d6d..ccbccc3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.1.0
+2.2.0