Allow AnimatedList as a child

[volgin]

I replaced:

final BoxScrollView child;

with

final AnimatedList child;

and everything worked like a charm. The problem, of course, is that I will have to remember to do it again when and if the plugin updates.

It will be nice to allow AnimatedList as a child. There is already child.scrollDirection == Axis.vertical, so passing any Widget with scrollDirection should work.