Fix Graph.set_previous with dict connection_map

Author: awentzonline

keras/layers/containers.py

@@ -129,7 +129,7 @@ def set_previous(self, layer, connection_map={}):
         else:
             if not connection_map:
                 raise Exception('Cannot attach multi-input layer: no connection_map provided.')
-            for k, v in connection_map:
+            for k, v in connection_map.items():
                 if k in self.inputs and v in layer.outputs:
                     self.inputs[k].set_previous(layer.outputs[v])
                 else: