leak libc from stack and then fastbin attack.

Exploit [here](https://github.com/0x01f/pwn_repo/blob/master/noxCTF2018_Grocery_List/hijack_hook.py)

Original writeup (https://github.com/0x01f/pwn_repo/blob/master/noxCTF2018_Grocery_List/hijack_hook.py).