Bump Bazel version to 2.2.0

Change-Id: I442f4d7a441fd504fce96c22c3c5680cf8e47225
diff --git a/.bazelversion b/.bazelversion
index 7ec1d6d..ccbccc3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.1.0
+2.2.0