fix goctl help message (#2414)

tools/goctl/api/cmd.go

@@ -43,7 +43,7 @@ var (
 
 	goCmd = &cobra.Command{
 		Use:   "go",
-		Short: "Generate go files for provided api in yaml file",
+		Short: "Generate go files for provided api in api file",
 		RunE:  gogen.GoCommand,
 	}