update preview image (#2)

thanks khoi!

Author: khoi

README.md

@@ -8,9 +8,7 @@ This is a simple Canvas-based game that requires a solid understanding of the pr
 
 Here's a walkthrough of implemented user stories.
 
-```
-<img src='http://http://g.recordit.co/cURdPMSHT2.gif' title='Video Walkthrough' width='' alt='Video Walkthrough' />
-```
+![](http://g.recordit.co/cURdPMSHT2.gif)
 
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