index.html: fixup top-level await usage.

public/index.html

@@ -9,10 +9,12 @@
   <video src=""></video>
 
   <script>
-    let video = document.querySelector('video')
-    let mediaStream = await navigator.mediaDevices.getDisplayMedia()
-    video.srcObject = mediaStream
-    video.play()
+    ;(async _ => {
+      let video = document.querySelector('video')
+      let mediaStream = await navigator.mediaDevices.getDisplayMedia()
+      video.srcObject = mediaStream
+      video.play()
+    })()
   </script>
 
 </body>