Bump Bazel version to 2.2.0

Change-Id: I2a5c850da123918a611ad63814681814d0ac08ad
diff --git a/.bazelversion b/.bazelversion
index 7ec1d6d..ccbccc3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.1.0
+2.2.0