Update APRDesign.html

Author: ckant787

docs/APRDesign.html

@@ -114,7 +114,7 @@ <h2>Directory Structure</h2>
 
 <p>Each type has a base directory.  Inside this base directory, are
 subdirectories, which contain the actual code.  These subdirectories are named
-after the platforms the are compiled on.  Unix is also used as a common
+after the platforms they are compiled on.  Unix is also used as a common
 directory.  If the code you are writing is POSIX based, you should look at the
 code in the unix directory.  A good rule of thumb, is that if more than half
 your code needs to be ifdef'ed out, and the structures required for your code