cmd/gobind: make sure to set exit code on type checking errors

Change-Id: Iea30db321c53b37b41a2b18689c5f724938a1593
Reviewed-on: https://go-review.googlesource.com/108135
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
diff --git a/cmd/gobind/main.go b/cmd/gobind/main.go
index c1f9490..6e6d239 100644
--- a/cmd/gobind/main.go
+++ b/cmd/gobind/main.go
@@ -141,7 +141,7 @@
 		var err error
 		typePkgs[i], err = imp.Import(pkg.ImportPath)
 		if err != nil {
-			fmt.Fprintf(os.Stderr, "%v\n", err)
+			errorf("%v\n", err)
 			return
 		}
 	}