Replace ${SHELL} with "$SHELL" to fix SC2086 (shellcheck)

ufetch-mxlinux

@@ -10,7 +10,7 @@ os="$(lsb_release -ds)"
 kernel="$(uname -sr)"
 uptime="$(uptime -p | sed 's/up //')"
 packages="$(dpkg -l | wc -l)"
-shell="$(basename ${SHELL})"
+shell="$(basename "$SHELL")"
 
 if [ -z "${WM}" ]; then
 	if [ "${XDG_CURRENT_DESKTOP}" ]; then