Bump Bazel version to 2.2.0

Change-Id: Id31d180c596c04e3e98b8a2c16de44cf89e04bbe
diff --git a/.bazelversion b/.bazelversion
index 7ec1d6d..ccbccc3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.1.0
+2.2.0