use 'npx kill-port' instead of killall (github#22007)

Author: peterbe

server.mjs

@@ -41,7 +41,9 @@ async function checkPortAvailability() {
   const portInUse = await portUsed.check(port)
   if (portInUse) {
     console.log(`\n\n\nPort ${port} is not available. You may already have a server running.`)
-    console.log('Try running `killall node` to shut down all your running node processes.\n\n\n')
+    console.log(
+      `Try running \`npx kill-port ${port}\` to shut down all your running node processes.\n\n\n`
+    )
     console.log('\x07') // system 'beep' sound
     process.exit(1)
   }