More consistent attribute setting

It turns out browsers convert `controls = true` into just `controls` in
the DOM, which is exactly what we want.

Author: csswizardry

demo/index.html

@@ -300,7 +300,7 @@ <h2><code>window.obs</code></h2>
         video.poster = './assets/poster.png';
         video.autoplay = true;
         video.muted = true;
-        video.setAttribute('controls', '');
+        video.controls = true;
         videoWrapper.appendChild(video);
       }