secret-handshake: fix broken link to source (#499)

Author: sjwarner-bp

exercises/secret-handshake/README.md

@@ -35,7 +35,7 @@ Note that, when trying to submit an exercise, make sure the exercise file that y
 For example, if you're submitting `bob.cs` for the Bob exercise, the submit command would be something like `exercism submit <path_to_exercism_dir>/csharp/bob/bob.cs`.
 ## Source
 
-Bert, in Mary Poppins [http://www.imdb.com/character/ch0011238/quotes](http://www.imdb.com/character/ch0011238/quotes)
+Bert, in Mary Poppins [http://www.imdb.com/title/tt0058331/quotes/qt0437047](http://www.imdb.com/title/tt0058331/quotes/qt0437047)
 
 ## Submitting Incomplete Solutions
 It's possible to submit an incomplete solution so you can see how others have completed the exercise.