Update build.func

fixes https://github.com/tteck/Proxmox/issues/2478

misc/build.func

@@ -340,7 +340,9 @@ advanced_settings() {
     echo -e "${DGN}Using Gateway IP Address: ${BGN}Default${CL}"
   fi
 
-  if [ "$var_os" != "alpine" ]; then
+  if [ "$var_os" == "alpine" ]; then
+    APT_CACHER=""
+  else
     if APT_CACHER_IP=$(whiptail --backtitle "Proxmox VE Helper Scripts" --inputbox "Set APT-Cacher IP (leave blank for default)" 8 58 --title "APT-Cacher IP" 3>&1 1>&2 2>&3); then
       APT_CACHER="${APT_CACHER_IP:+yes}"
       echo -e "${DGN}Using APT-Cacher IP Address: ${BGN}${APT_CACHER_IP:-Default}${CL}"