SuperHero Class - Guardians of the Galaxy

Missing a test for an attack method

```javascript
//TEST AN ATTACK METHOD
QUnit.test("Wolverine attacks Gamora", function(assert) {
    wolverine.attack(gamora);
    assert.strictEqual(gamora.health, (100 - wolverine.strength), "Wolverine attacking Gamora should drop her health to 50");
});
```