change page navigation

lib/pages/signin/signup_page.dart

@@ -2,6 +2,7 @@ import 'package:fcs/pages/main/model/main_model.dart';
 import 'package:fcs/pages/main/util.dart';
 import 'package:fcs/pages/widgets/local_text.dart';
 import 'package:fcs/pages/widgets/progress.dart';
+import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:font_awesome_flutter/font_awesome_flutter.dart';
@@ -32,7 +33,9 @@ class _SignupPageState extends State<SignupPage> {
         appBar: AppBar(
           centerTitle: true,
           leading: new IconButton(
-            icon: new Icon(Icons.close),
+            icon: new Icon(
+              CupertinoIcons.back,
+            ),
             onPressed: () => Navigator.of(context).pop(),
           ),
           backgroundColor: primaryColor,