Update check for Keras type

Signed-off-by: Beat Buesser <[email protected]>

Author: Beat Buesser

art/estimators/classification/keras.py

@@ -126,9 +126,9 @@ def __init__(
         self._input_layer = input_layer
         self._output_layer = output_layer
 
-        if "<class 'tensorflow" in str(type(model)):
+        if "<class 'tensorflow" in str(type(model).__mro__):
             self.is_tensorflow = True
-        elif "<class 'keras" in str(type(model)):
+        elif "<class 'keras" in str(type(model).__mro__):
             self.is_tensorflow = False
         else:
             raise TypeError("Type of model not recognized:" + str(type(model)))