Segfault on f-string in ast3

[ilevkivskyi]

This happens:

Python 3.5.1 |Anaconda custom (x86_64)| (default, Dec  7 2015, 11:24:55) 
[GCC 4.2.1 (Apple Inc. build 5577)] on darwin

>>> from typed_ast import ast3
>>> ast3.parse("x = f'Hi {x}'")
Segmentation fault: 11

Unfortunately, I could not test this on other versions of Python now.

[ilevkivskyi]

I discovered it fails even on correct f-strings:

>>> ast3.parse("x = 3; f'Hi {x}'")
Segmentation fault: 11

f-strings without variables inside are parsed correctly without error.

[refi64]

I remember this had happened in #22, but I don't remember what I did to fix it...

[ilevkivskyi]

OK, found it, here is the fix #32