Upgrade protobuf to v3.6.1

Merge commit 'be9845eb2abf508c86da76321b4e2c352b45b532' into master

Change-Id: I1b3cd2e177686afe95f44abc4fb0c6f9e001e784
diff --git a/WORKSPACE b/WORKSPACE
index e794adb..30cb782 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -302,3 +302,7 @@
     ],
 )
 
+local_repository(
+    name = "com_google_protobuf",
+    path = "third_party/protobuf",
+)