cmd/gobind: fix missing parameter for formatting

Change-Id: I89256a18a9aeb2f32808f391258c8f66690e5247
Reviewed-on: https://go-review.googlesource.com/87716
Reviewed-by: Elias Naur <elias.naur@gmail.com>
diff --git a/cmd/gobind/gen.go b/cmd/gobind/gen.go
index 27f71fb..28ee405 100644
--- a/cmd/gobind/gen.go
+++ b/cmd/gobind/gen.go
@@ -79,7 +79,7 @@
 		if p == nil {
 			p, err := build.Default.Import("golang.org/x/mobile/bind", ".", build.ImportComment)
 			if err != nil {
-				errorf(`"golang.org/x/mobile/bind" is not found; run go get golang.org/x/mobile/bind: %v`)
+				errorf(`"golang.org/x/mobile/bind" is not found; run go get golang.org/x/mobile/bind: %v`, err)
 				return
 			}
 			repo := filepath.Clean(filepath.Join(p.Dir, "..")) // golang.org/x/mobile directory.