Fix lr setting of param_attr in Fluid

python/paddle/v2/fluid/param_attr.py

@@ -58,7 +58,9 @@ class ParamAttr(object):
     def to_kwargs(self, with_initializer=False):
         kwargs = {
             'name': self.name,
-            'learning_rate': self.learning_rate,
+            'optimize_attr': {
+                'learning_rate': self.learning_rate
+            },
             'regularizer': self.regularizer,
             'trainable': self.trainable,
             'clip_attr': self.clip