Upgrading samples to flutter_lints, part 1 of n (#804)

provider_shopper/lib/screens/login.dart

@@ -10,7 +10,7 @@ class MyLogin extends StatelessWidget {
     return Scaffold(
       body: Center(
         child: Container(
-          padding: EdgeInsets.all(80.0),
+          padding: const EdgeInsets.all(80.0),
           child: Column(
             mainAxisAlignment: MainAxisAlignment.center,
             children: [
@@ -19,21 +19,21 @@ class MyLogin extends StatelessWidget {
                 style: Theme.of(context).textTheme.headline1,
               ),
               TextFormField(
-                decoration: InputDecoration(
+                decoration: const InputDecoration(
                   hintText: 'Username',
                 ),
               ),
               TextFormField(
-                decoration: InputDecoration(
+                decoration: const InputDecoration(
                   hintText: 'Password',
                 ),
                 obscureText: true,
               ),
-              SizedBox(
+              const SizedBox(
                 height: 24,
               ),
               ElevatedButton(
-                child: Text('ENTER'),
+                child: const Text('ENTER'),
                 onPressed: () {
                   Navigator.pushReplacementNamed(context, '/catalog');
                 },