Make Variable support for future.division.

python/paddle/fluid/layers/math_op_patch.py

@@ -169,7 +169,9 @@ def monkey_patch_variable():
             # a*b == b*a. Do not need to reverse explicitly
         ("__rmul__", "elementwise_mul", False),
         ("__div__", "elementwise_div", False),
+        ("__truediv__", "elementwise_div", False),
         ("__rdiv__", "elementwise_div", True),
+        ("__rtruediv__", "elementwise_div", True),
         ("__pow__", "elementwise_pow", False),
         ("__rpow__", "elementwise_pow", True),
             # for logical compare