Revert "Ch06: Fix link to script source"

This reverts commit 5fc8cc2.

Author: KtorZ

ch06.md

@@ -167,7 +167,7 @@ And we're done!
 <img src="images/cats_ss.png" alt="cats grid" />
 
 Here is the finished script:
-[include](https://github.com/MostlyAdequate/mostly-adequate-guide/blob/master/exercises/ch06/main.js)
+[include](./exercises/ch06/main.js)
 
 Now look at that. A beautifully declarative specification of what things are, not how they come to be. We now view each line as an equation with properties that hold. We can use these properties to reason about our application and refactor.