Use the unminified version of video.js

The minified 4.x build mangles "preload" passed in as options, which prevents it being overridden in data-setup or through the video element attribute. Switch to the dev version so that preload settings can be adjusted.

@@ -7,7 +7,7 @@
   <link href="node_modules/video.js/dist/video-js/video-js.css" rel="stylesheet">
 
   <!-- video.js -->
-  <script src="node_modules/video.js/dist/video-js/video.js"></script>
+  <script src="node_modules/video.js/dist/video-js/video.dev.js"></script>
 
   <!-- Media Sources plugin -->
   <script src="node_modules/videojs-contrib-media-sources/src/videojs-media-sources.js"></script>