cmd: fix go.mod files

Change-Id: I13cbb878dad1024bc1b5e07e9c10f53cacce0349
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/178717
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>

cmd/protoc-gen-go-grpc/testdata/go.mod

@@ -1,7 +1,7 @@
 module google.golang.org/protobuf/cmd/protoc-gen-go-grpc/testdata
 
 require (
-	github.com/golang/protobuf v1.2.1-0.20190516215712-ae2eaafab405
+	github.com/golang/protobuf v1.2.1-0.20190523175523-a1331f0b4ab4
 	google.golang.org/grpc v1.19.0
 	google.golang.org/protobuf v1.0.0
 )

cmd/protoc-gen-go/testdata/go.mod

@@ -1,7 +1,7 @@
 module google.golang.org/protobuf/cmd/protoc-gen-go/testdata
 
 require (
-	github.com/golang/protobuf v1.2.1-0.20190516215712-ae2eaafab405
+	github.com/golang/protobuf v1.2.1-0.20190523175523-a1331f0b4ab4
 	google.golang.org/protobuf v1.0.0
 )