Merge pull request #1889 from twmht/import_lion

import lion in __init__.py

Author: rwightman

timm/optim/__init__.py

@@ -13,4 +13,5 @@
 from .radam import RAdam
 from .rmsprop_tf import RMSpropTF
 from .sgdp import SGDP
+from .lion import Lion
 from .optim_factory import create_optimizer, create_optimizer_v2, optimizer_kwargs