Fixed center problem of buttons. (#459)

* Fixed center problem of buttons of the issue #458

* Fixed center problem of buttons of the issue #458 for toast_context page

example/android/build.gradle

@@ -26,6 +26,6 @@ subprojects {
     project.evaluationDependsOn(':app')
 }
 
-task clean(type: Delete) {
+tasks.register("clean", Delete) {
     delete rootProject.buildDir
 }

example/lib/main.dart

@@ -25,29 +25,31 @@ class _MyAppState extends State<MyApp> {
       appBar: AppBar(
         title: Text("Toast"),
       ),
-      body: Column(
-        mainAxisAlignment: MainAxisAlignment.center,
-        children: [
-          ElevatedButton(
-            onPressed: () {
-              Navigator.of(context).push(MaterialPageRoute(
-                builder: (context) => ToastNoContext(),
-              ));
-            },
-            child: Text("Flutter Toast No Context"),
-          ),
-          SizedBox(
-            height: 24.0,
-          ),
-          ElevatedButton(
-            onPressed: () {
-              Navigator.of(context).push(MaterialPageRoute(
-                builder: (context) => ToastContext(),
-              ));
-            },
-            child: Text("Flutter Toast Context"),
-          ),
-        ],
+      body: Center(
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            ElevatedButton(
+              onPressed: () {
+                Navigator.of(context).push(MaterialPageRoute(
+                  builder: (context) => ToastNoContext(),
+                ));
+              },
+              child: Text("Flutter Toast No Context"),
+            ),
+            SizedBox(
+              height: 24.0,
+            ),
+            ElevatedButton(
+              onPressed: () {
+                Navigator.of(context).push(MaterialPageRoute(
+                  builder: (context) => ToastContext(),
+                ));
+              },
+              child: Text("Flutter Toast Context"),
+            ),
+          ],
+        ),
       ),
     );
   }

example/lib/toast_context.dart

@@ -139,60 +139,62 @@ class _ToastContextState extends State<ToastContext> {
       appBar: AppBar(
         title: Text("Custom Toasts"),
       ),
-      body: Column(
-        children: [
-          SizedBox(
-            height: 24.0,
-          ),
-          ElevatedButton(
-            child: Text("Show Custom Toast"),
-            onPressed: () {
-              _showToast();
-            },
-          ),
-          ElevatedButton(
-            child: Text("Show Custom Toast via PositionedToastBuilder"),
-            onPressed: () {
-              _showBuilderToast();
-            },
-          ),
-          SizedBox(
-            height: 24.0,
-          ),
-          ElevatedButton(
-            child: Text("Custom Toast With Close Button"),
-            onPressed: () {
-              _showToastCancel();
-            },
-          ),
-          SizedBox(
-            height: 24.0,
-          ),
-          ElevatedButton(
-            child: Text("Queue Toasts"),
-            onPressed: () {
-              _queueToasts();
-            },
-          ),
-          SizedBox(
-            height: 24.0,
-          ),
-          ElevatedButton(
-            child: Text("Cancel Toast"),
-            onPressed: () {
-              _removeToast();
-            },
-          ),
-          SizedBox(
-            height: 24.0,
-          ),
-          ElevatedButton(
-            child: Text("Remove Queued Toasts"),
-            onPressed: () {
-              _removeAllQueuedToasts();
-            },
-          ),
-        ],
+      body: Center(
+        child: Column(
+          children: [
+            SizedBox(
+              height: 24.0,
+            ),
+            ElevatedButton(
+              child: Text("Show Custom Toast"),
+              onPressed: () {
+                _showToast();
+              },
+            ),
+            ElevatedButton(
+              child: Text("Show Custom Toast via PositionedToastBuilder"),
+              onPressed: () {
+                _showBuilderToast();
+              },
+            ),
+            SizedBox(
+              height: 24.0,
+            ),
+            ElevatedButton(
+              child: Text("Custom Toast With Close Button"),
+              onPressed: () {
+                _showToastCancel();
+              },
+            ),
+            SizedBox(
+              height: 24.0,
+            ),
+            ElevatedButton(
+              child: Text("Queue Toasts"),
+              onPressed: () {
+                _queueToasts();
+              },
+            ),
+            SizedBox(
+              height: 24.0,
+            ),
+            ElevatedButton(
+              child: Text("Cancel Toast"),
+              onPressed: () {
+                _removeToast();
+              },
+            ),
+            SizedBox(
+              height: 24.0,
+            ),
+            ElevatedButton(
+              child: Text("Remove Queued Toasts"),
+              onPressed: () {
+                _removeAllQueuedToasts();
+              },
+            ),
+          ],
+        ),
       ),
     );
   }