Bump Bazel version to 2.2.0

Change-Id: If884406de227db58e809f3dfba2e2d83428962c4

.bazelversion

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