Bump Bazel version to 2.2.0

Change-Id: I99ff8e092876995f26eafaa9f856b7fb43ab30e9
diff --git a/.bazelversion b/.bazelversion
index 7ec1d6d..ccbccc3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.1.0
+2.2.0