[pacman] Add pikaur to list of AUR helpers that handle SUID

`pikaur` (https://github.com/actionless/pikaur) handles sudo
authentication itself.

Closes #302

modules/pacman/init.zsh

@@ -24,7 +24,7 @@ elif (( ! ${+commands[${zpacman_frontend}]} )); then
 You can fix this error by editing the 'zpacman_frontend' variable in your .zimrc" >&2
   zpacman_frontend='pacman'
   zpacman_frontend_priv='sudo pacman'
-elif [[ ${zpacman_frontend} == ("yaourt"|"pacaur"|"yay") ]]; then
+elif [[ ${zpacman_frontend} == ("yaourt"|"pacaur"|"yay"|"pikaur") ]]; then
   # those AUR helpers handle SUID themselves
   zpacman_frontend_priv="${zpacman_frontend}"
 else