index.html: Move to larger video to test if frameworks can handle it.

The video is 1920 x 1080 which means that centered CSS themes will need a
special rule to resize the video to fit inside the margin. From early
testing only a few of the CSS dropins correctly handle this, awsm.css
being one of them.

index.html

@@ -247,8 +247,7 @@
             <h2>Video</h2>
             <div>
               <video controls>
-                <source src="https://github.com/benhosmer/HTML5-Test-Videos/blob/master/big_buck_bunny.mp4?raw=true" type="video/mp4">
-                <source src="https://github.com/benhosmer/HTML5-Test-Videos/blob/master/big_buck_bunny.ogv?raw=true" type="video/ogg">
+                <source src="bird.mp4" type="video/mp4">
               </video>
             </div>
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