irclib.py: fix an encoding error with Python 3 and SASL ECDSA-NIST256P-CHALLENGE
irclib.py: fix an encoding error with Python 3 and SASL ECDSA-NIST256P-CHALLENGE

Closes ProgVal#1028.

Ban3/Limnoria,ProgVal/Limnoria-test,ProgVal/Limnoria-test,Ban3/Limnoria