add HelpWriter and ErrorWriter (#2)

* add HelpWriter and ErrorWriter

Author: sergiy-petrov

sql-migrate/main.go

@@ -38,8 +38,10 @@ func realMain() int {
 				return &SkipCommand{}, nil
 			},
 		},
-		HelpFunc: cli.BasicHelpFunc("sql-migrate"),
-		Version:  GetVersion(),
+		HelpFunc:    cli.BasicHelpFunc("sql-migrate"),
+		HelpWriter:  os.Stdout,
+		ErrorWriter: os.Stderr,
+		Version:     GetVersion(),
 	}
 
 	exitCode, err := cli.Run()