message: Update merge-two-binary-trees.py
  Added self for recursive calls
diff: @@ -48,6 +48,6 @@ class Solution(object):
  if t2 is None:
  return t1
  t1.val += t2.val
  - t1.left = mergeTrees(t1.left, t2.left)
  - t1.right = mergeTrees(t1.right, t2.right)
  + t1.left = self.mergeTrees(t1.left, t2.left)
  + t1.right = self.mergeTrees(t1.right, t2.right)
  return t1
  