Improved error message if results are unexpected

When adding a different reporter to `configureAxe` it created an error for this library. While the library shouldn't support different reporters we should warn the
user when they do.

Author: zcolleyz

index.js

@@ -123,7 +123,9 @@ function filterViolations(violations, impactLevels) {
 const toHaveNoViolations = {
   toHaveNoViolations(results) {
     if (typeof results.violations === "undefined") {
-      throw new Error("No violations found in aXe results object");
+      throw new Error(
+        "Unexpected aXe results object. No violations property found.\nDid you change the `reporter` in your aXe configuration?"
+      );
     }
 
     const violations = filterViolations(