fixup! tweak imports

nifty5/models/variable.py

@@ -10,7 +10,7 @@ class Variable(Model):
         super(Variable, self).__init__(position)
 
         self._value = position
-        self._gradient = ift.ScalingOperator(1., position.domain)
+        self._gradient = ScalingOperator(1., position.domain)
 
     def at(self, position):
         return self.__class__(position)