Update gRPC version to 1.14. (#1404)

* Update gRPC version to 0.14.

* Fix fingbugs warning.

* Add more comments about the workaround.
diff --git a/build.gradle b/build.gradle
index 07e4f8d..14c5211 100644
--- a/build.gradle
+++ b/build.gradle
@@ -149,7 +149,7 @@
         findBugsAnnotationsVersion = '3.0.1'
         findBugsJsr305Version = '3.0.2'
         errorProneVersion = '2.3.1'
-        grpcVersion = '1.12.0'
+        grpcVersion = '1.14.0'
         guavaVersion = '20.0'
         googleAuthVersion = '0.10.0'
         googleCloudBetaVersion = '0.58.0-beta'