fix: update isProperFraction to return false for zero denominator instead of throwing an error

Author: CatchingKiyoko

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

@@ -8,9 +8,7 @@
 // write one test at a time, and make it pass, build your solution up methodically
 
 function isProperFraction(numerator, denominator) {
-  if (denominator === 0) {
-    throw new Error();
-  }
+  if (denominator === 0) return false; // avoid division by zero
   return Math.abs(numerator) < Math.abs(denominator);
 }