PEP8 DoubleOp in the documentation.

doc/cifarSC2011/extending_theano.txt

@@ -108,13 +108,17 @@ Op example
     class DoubleOp(theano.Op):
         def __eq__(self, other):
             return type(self) == type(other)
+
         def __hash__(self):
             return hash(type(self))
+
         def __str__(self):
             return self.__class__.__name__
+
         def make_node(self, x):
             x = theano.tensor.as_tensor_variable(x)
             return theano.Apply(self, [x], [x.type()])
+
         def perform(self, node, inputs, output_storage):
             x = inputs[0]
             z = output_storage[0]