Bump Bazel version to 2.2.0

Change-Id: Icfe978e45ffbe2804f42bf49f3b493eeaf57fb60
diff --git a/.bazelversion b/.bazelversion
index 7ec1d6d..ccbccc3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.1.0
+2.2.0