fix(script): Treat '@' and '+' in pkg names, ZFS doesn't like them (#3)

Replace at characters ('@') indiscriminately with one dot each ('.'),
replace plus characters ('+') with one underscore each ('_').

pacman-zfs-snapshot.sh

@@ -359,6 +359,8 @@ function do_retention () {
 function main () {
     local pkgs_in_transaction
     pkgs_in_transaction=("${@}")
+    pkgs_in_transaction=("${pkgs_in_transaction[@]//+/_}")
+    pkgs_in_transaction=("${pkgs_in_transaction[@]//@/.}")
 
     local -a important_pkgs_in_transaction trivial_pkgs_in_transaction
     split_pkgs_by_importance "${pkgs_in_transaction[@]}"