Bump Bazel version to 2.2.0

Change-Id: I930955a253292c10707bcbbe52ab5d0c137bf5e3
diff --git a/.bazelversion b/.bazelversion
index 7ec1d6d..ccbccc3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.1.0
+2.2.0