Replace deprecated accentColor with colorScheme.secondary

Author: danvick

example/lib/sources/complete_form.dart

@@ -260,7 +260,7 @@ class CompleteFormState extends State<CompleteForm> {
               children: <Widget>[
                 Expanded(
                   child: MaterialButton(
-                    color: Theme.of(context).accentColor,
+                    color: Theme.of(context).colorScheme.secondary,
                     onPressed: () {
                       if (_formKey.currentState?.saveAndValidate() ?? false) {
                         print(_formKey.currentState?.value);
@@ -281,10 +281,10 @@ class CompleteFormState extends State<CompleteForm> {
                     onPressed: () {
                       _formKey.currentState?.reset();
                     },
-                    // color: Theme.of(context).accentColor,
+                    // color: Theme.of(context).colorScheme.secondary,
                     child: Text(
                       'Reset',
-                      style: TextStyle(color: Theme.of(context).accentColor),
+                      style: TextStyle(color: Theme.of(context).colorScheme.secondary),
                     ),
                   ),
                 ),

example/lib/sources/signup_form.dart

@@ -103,7 +103,7 @@ class _SignupFormState extends State<SignupForm> {
                 ),
                 const SizedBox(height: 10),
                 MaterialButton(
-                  color: Theme.of(context).accentColor,
+                  color: Theme.of(context).colorScheme.secondary,
                   onPressed: () {
                     if (_formKey.currentState?.saveAndValidate() ?? false) {
                       print('Valid');