improved error msg on toBeRehectedWithError and all other built-in async matchers

spec/core/matchers/async/toBeRejectedWithSpec.js

@@ -83,7 +83,7 @@ describe('#toBeRejectedWith', function() {
     }
 
     expect(f).toThrowError(
-      'Expected toBeRejectedWith to be called on a promise.'
+      `Expected toBeRejectedWith to be called on a promise but was on a ${typeof actual}.`
     );
   });
 });