+1 animations triggering on all inner grid rebuilds

[Zambrella]

This is happening because the animation controller.forward() is set in the build method (which is obviously bad). However, I cannot think of where else to 'listen' to the change in winning state of an inner grid in a way that only triggers once.

[slovnicki]

@Zambrella here's a solution: https://github.com/Flutter-Buddies/tic_tac_no/commit/4b537e6418d8668f1e2bd6987f9ffc0a54defe65