Update example following new op.

doc/library/typed_list.txt

@@ -27,9 +27,10 @@ as outputs).::
     import theano.typed_list
 
     a = theano.typed_list.TypedListType(theano.tensor.fvector)()
+    l = theano.typed_list.length(a)
     s, _ = theano.scan(fn=lambda i, tl: tl[i].sum(),
                        non_sequences=[a],
-                       sequences=[theano.tensor.arange(2, dtype='int64')])
+                       sequences=[theano.tensor.arange(l, dtype='int64')])
 
     f = theano.function([a], s)
     f([[1, 2, 3], [4, 5]])