[fbsync] Add MovingMNIST to __all__ list in datasets (#8705)

Reviewed By: vmoens

Differential Revision: D68021973

fbshipit-source-id: 3bbe86bf80dfb76456fffdac60a812a432d2a5f2

Author: NicolasHug

torchvision/datasets/__init__.py

@@ -72,6 +72,7 @@
     "QMNIST",
     "MNIST",
     "KMNIST",
+    "MovingMNIST",
     "StanfordCars",
     "STL10",
     "SUN397",