Fix link (#596)

Author: rasbt

ch03/README.md

@@ -18,4 +18,4 @@ In the video below, I provide a code-along session that covers some of the chapt
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-[![Link to the video](https://img.youtube.com/vi/-Ll8DtpNtvk/0.jpg)](https://www.youtube.com/watch?v=Ll8DtpNtvk)
+[![Link to the video](https://img.youtube.com/vi/-Ll8DtpNtvk/0.jpg)](https://www.youtube.com/watch?v=-Ll8DtpNtvk)