Update article.md

Author: leviding

1-js/03-code-quality/05-testing-mocha/article.md

@@ -160,7 +160,7 @@ We can select one of two ways to organize the test here:
       });
 
       it("3 raised to power 3 is 27", function() {
-        assert.equal(pow(3, 3), 27);
+        assert.equal(pow(3, 4), 81);
       });
 
     });