Bump Bazel version to 2.2.0

Change-Id: I60ea4e2eac8a634ee55fdb0b19c3f88e967adbcb
diff --git a/.bazelversion b/.bazelversion
index 7ec1d6d..ccbccc3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.1.0
+2.2.0