Bump Bazel version to 2.2.0

Change-Id: I61c84e8e4bcd4679be993d6f2e51e99959d3aba1
diff --git a/.bazelversion b/.bazelversion
index 7ec1d6d..ccbccc3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-2.1.0
+2.2.0