added "module.exports" so jest can find the function

Author: CatchingKiyoko

Sprint-3/1-implement-and-rewrite-tests/implement/2-is-proper-fraction.js

@@ -54,3 +54,5 @@ assertEquals(equalFraction, false);
 
 // Stretch:
 // What other scenarios could you test for?
+
+module.exports = isProperFraction;