Updated doctests.

line.py

@@ -15,7 +15,7 @@ def generate_line(root):
     >>> plus2 = Node('+', l0, l1)
     >>> times = Node('*', plus, plus2)
     >>> print generate_line(times)
-    (1 + 2) * (1 + 2)
+    (1 + 2)(1 + 2)
 
     >>> l2 = Leaf(3)
     >>> uminus = Node('-', l2)