src/conf.py: follow nick changes

followIdentificationThroughNickChanges is now True.

I am not sure what the "little greater security" of previous `config
help` meant, but False appears to make NickAuth automatically unidentify
you when user changes their nick and this possibly also affects GPG.

I can see that I asked about it by grepping logs, but I cannot find
answer from them as most of results come from Limnoria which is replying
to `config list supybot`.

I have also seen confused users on some channels wondering about having to
identify again after changing their nick.