cmd/protoc-gen-go: --version should exit 0

Fixes golang/protobuf#1153.

Change-Id: Id2ada2353413c3371e677dcf3fdfa6fdc24a3c56
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/239339
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
diff --git a/cmd/protoc-gen-go/main.go b/cmd/protoc-gen-go/main.go
index 55a58df..a354df9 100644
--- a/cmd/protoc-gen-go/main.go
+++ b/cmd/protoc-gen-go/main.go
@@ -24,7 +24,7 @@
 func main() {
 	if len(os.Args) == 2 && os.Args[1] == "--version" {
 		fmt.Fprintf(os.Stderr, "%v %v\n", filepath.Base(os.Args[0]), version.String())
-		os.Exit(1)
+		os.Exit(0)
 	}
 
 	var (