Example app is not working

Hello!

Tried running the example, could not. Here is what fixed it for me:

```patch
diff --git a/lib/src/app.dart b/lib/src/app.dart
index 7cdc637..5927d7b 100644
--- a/lib/src/app.dart
+++ b/lib/src/app.dart
@@ -159,7 +159,7 @@ class Application extends Widget {
data: MediaQueryData(size: mediaSize),
child: Builder(
builder: (context) => Theme(
- data: theme(context),
+ data: theme ?? ThemeData.base(context),
child:
builder != null ? builder(context, currentRoute) : currentRoute,
),
```

A quick `git apply` to this and you are golden ;)