Bump Bazel version to 2.2.0

Change-Id: I650b7561aa9ece1d48eeff56c79a7aec34eb8a42
diff --git a/.bazelversion b/.bazelversion
index 7ec1d6d..ccbccc3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.1.0
+2.2.0