Bump Bazel version to 2.2.0

Change-Id: I4c6563329e3988034501735f62e0a560244b7f7a
diff --git a/.bazelversion b/.bazelversion
index 7ec1d6d..ccbccc3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.1.0
+2.2.0