Metronome item gen diff

Fixed https://github.com/po-devs/pokemon-online/pull/958

Cleaner fix that actually fixes. 
```
if (b.gen() >= 5) {
    count += 2;
} else {
    count += 1;
}
if (count > 10) {
    count = 10;
} 
```
Would be fixing it the way you were trying to explain. 

If you set count to 10 immediately, you double the attack, cause ItemMod2Modifier adds 10 automatically when calculating damage. So the 2nd use of an attack would be 10 + 10 = double your damage on turn 1. Turn 5 would be triple damage.