Fix stylistic issue

Expand variable using ${FTLconf}

Signed-off-by: Ludovic Rousseau <ludovic.rousseau@free.fr>

advanced/Scripts/piholeLogFlush.sh

@@ -17,7 +17,7 @@ source ${colfile}
 # a) the setting is not present in the config file, or
 # b) the setting is commented out (e.g. "#DBFILE=...")
 FTLconf="/etc/pihole/pihole-FTL.conf"
-[ -e "$FTLconf" ] && DBFILE="$(sed -n -e 's/^\s*DBFILE\s*=\s*//p' $FTLconf)"
+[ -e "$FTLconf" ] && DBFILE="$(sed -n -e 's/^\s*DBFILE\s*=\s*//p' ${FTLconf})"
 # Test for empty string. Use standard path in this case.
 if [ -z "$DBFILE" ]; then
   DBFILE="/etc/pihole/pihole-FTL.db"