Fix post add button color on home screen

lib/screens/home.dart

@@ -80,7 +80,10 @@ class _HomeScreenState extends State<HomeScreen> {
             onPressed: () {
               context.push('/post/new');
             },
-            icon: Icon(Icons.add),
+            icon: Icon(
+              Icons.add,
+              color: Theme.of(context).primaryColor,
+            ),
           ),
         ],
       ),