Update extending_theano tutorial

doc/tutorial/extending_theano.txt

@@ -202,7 +202,6 @@ Other methods can be optionally defined by the op.
   Given to the method :func:`__hash__` automatically generated from
   :attr:`__props__`, two ops will be have the same hash if they have the same
   values for all the properties listed in :attr:`__props__`.
-
   :attr:`__props__` will also generate a  suitable :func:`__str__` for your op.
   This requires development version after September 1st, 2014 or version 0.7.