Fix redefining aliases that uses import typing

[aklajnert]

This is an attempt to solve #25. I'm not sure if that's the best solution, however, it works and it's pretty easy.

The problem was that actual node object had 3 children: typing (Leaf), .Optional (Node) and [str] (Node), and expected object only 2 children: typing.Optional (Leaf), [str] (Node), which made them not equal. No idea why the same file is parsed differently, but the proposed solution ignores that problem.

[aklajnert]

Actually it doesn't work for more complex types, and the usage of typing.* seems to not be the factor that causes the issue:

Expected: 'Union[str, bytes, None, List[Union[str, bytes]], Tuple[Union[str, bytes], ...]]', 
actual:   'Union[ str, bytes, None, List[Union[str, bytes]], Tuple[Union[str, bytes], ...],\n]'

I'll try to figure it out later. Any hints on how to tackle that @ambv?