Fix a typo syscanll.SIGTERM -> syscall.SIGTERM (#1868)

README.md

@@ -1696,7 +1696,7 @@ func main() {
 	// Wait for interrupt signal to gracefully shutdown the server with
 	// a timeout of 5 seconds.
 	quit := make(chan os.Signal)
-	// kill (no param) default send syscanll.SIGTERM
+	// kill (no param) default send syscall.SIGTERM
 	// kill -2 is syscall.SIGINT
 	// kill -9 is syscall.SIGKILL but can"t be catch, so don't need add it
 	signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)