convert both $rx and $tx in one call to numfmt (#1082)

see numfmt(1) for details

.local/bin/statusbar/sb-nettraf

@@ -26,4 +26,4 @@ update() {
 rx=$(update /sys/class/net/[ew]*/statistics/rx_bytes)
 tx=$(update /sys/class/net/[ew]*/statistics/tx_bytes)
 
-printf "🔻%4sB 🔺%4sB\\n" $(numfmt --to=iec $rx) $(numfmt --to=iec $tx)
+printf "🔻%4sB 🔺%4sB\\n" $(numfmt --to=iec $rx $tx)