Fix Yogi import (tensorflow#875)

seanpmorgan · WindQAQ · commit 0a23fd2dc41b · 2020-01-14T08:15:04.000-08:00
diff --git a/tensorflow_addons/optimizers/__init__.py b/tensorflow_addons/optimizers/__init__.py
@@ -39,3 +39,4 @@
 from tensorflow_addons.optimizers.weight_decay_optimizers import SGDW
 from tensorflow_addons.optimizers.weight_decay_optimizers import (
     extend_with_decoupled_weight_decay)
+from tensorflow_addons.optimizers.yogi import Yogi
