Bug fix: concatenation error in 04-bof_variable/csaw18_boi/exploit.py

[vilroi]

I have encountered the following error when running exploit.py for 04-bof_variable/csaw18_boi, and am submitting a fix.

vilroi@nightmare:~/nightmare/modules/04-bof_variable/csaw18_boi$ python3 exploit.py 
[+] Starting local process './boi': pid 6900
Traceback (most recent call last):
  File "/home/vilroi/nightmare/modules/04-bof_variable/csaw18_boi/exploit.py", line 11, in <module>
    payload = "0"*0x14  + p32(0xcaf3baee)
              ~~~~~~~~~~^~~~~~~~~~~~~~~~~
TypeError: can only concatenate str (not "bytes") to str
[*] Stopped process './boi' (pid 6900)