Changing the cache duration (maxAgeCacheObject of the CacheManager)

Is it possible to change the cache duration easily?

I see that `BaseCacheManager` has default cache duration as 30 days (`Duration maxAgeCacheObject = const Duration(days: 30)`), but I would like to have the cache duration as 30 minutes.

I tried to create a new cache manager, which extends `BaseCacheManager` and overwrites the `maxAgeCacheObject`

```
class ImageCacheManager extends BaseCacheManager {
static const key = "libCachedImageData";

static ImageCacheManager _instance;

/// The DefaultCacheManager that can be easily used directly. The code of
/// this implementation can be used as inspiration for more complex cache
/// managers.
factory ImageCacheManager() {
if (_instance == null) {
_instance = new ImageCacheManager._();
}
return _instance;
}

ImageCacheManager._() : super(key, maxAgeCacheObject: Duration(minutes: 30));

Future getFilePath() async {
var directory = await getTemporaryDirectory();
return p.join(directory.path, key);
}
}
```

But still, the images are being cached for more than 30 minutes.