Fixed linter issue

Author: vicajilau

open_file_mac/example/lib/main.dart

@@ -1,11 +1,8 @@
-
-import 'package:flutter/material.dart';
 import 'dart:async';
 
+import 'package:flutter/material.dart';
 import 'package:open_file_mac/open_file_mac.dart';
 
-
-
 void main() => runApp(MyApp());
 
 class MyApp extends StatefulWidget {
@@ -17,13 +14,13 @@ class _MyAppState extends State<MyApp> {
   var _openResult = 'Unknown';
 
   Future<void> openFile() async {
-    final result = await OpenFileMac().open("/Users/chendong/Downloads/R-C.jpeg");
+    final result =
+        await OpenFileMac().open("/Users/chendong/Downloads/R-C.jpeg");
     setState(() {
       _openResult = "type=${result.type}  message=${result.message}";
     });
   }
 
-
   @override
   Widget build(BuildContext context) {
     return MaterialApp(