refactor: change alternate url for embed video file (#1579)

Author: kungfux

_includes/embed/video.html

@@ -32,7 +32,7 @@
 
 <p>
   <video class="embed-video file" src="{{ video_url }}" {{ poster }} {{ attributes }}>
-    Your browser doesn't support HTML video. Here is a <a href="{{ url }}">link to the video</a> instead.
+    Your browser doesn't support HTML video. Here is a <a href="{{ video_url }}">link to the video</a> instead.
   </video>
   <em>{{ include.title }}</em>
 </p>