display.sh: fixed separator implementation

lib/display.sh

@@ -130,10 +130,12 @@ separator()
 {
     echo -ne "$BYellow"
     local i=0
-    for i in {1..$(( $(tput cols) - 1 ))}; do
+    declare -li length=$(( $(tput cols) - 1 ))
+    for i in $(seq 1 $length); do
         echo -n "-"
     done
     echo -e "$DEFAULTCOL"
+    unset i length
 }
 export -f separator