VOL-2020 re-release to get proper version tag; add go.mod file

Change-Id: I97af22349c731d953ec8e5cc7db2c3a38fce9fc7
diff --git a/Makefile b/Makefile
index 6e472a3..c34fb7e 100644
--- a/Makefile
+++ b/Makefile
@@ -114,6 +114,7 @@
 
 go-test: protoc_check
 	test/test-go-proto-consistency.sh
+	GO111MODULE=on go mod verify
 
 go-clean:
 	rm -rf go_temp