Replace profitux link with migadu after migration

Goodbye, Profitux; you've been serving us well!

dotfiles/config/bmo/wish.ini

     tor     = https://theoldreader.com/
     tw      = https://twitter.com/
     w       = http://en.wikipedia.org/
-    wpc     = https://webmail.profitux.cz/
+    wmc     = https://webmail.migadu.com/
     xkcd    = http://xkcd.com/
     yt      = https://www.youtube.com/
     zoo     = http://www.zooborns.com/