Mob healthbars should round up the box number

This changes the rounding strategy from truncation to ceiling.

```
Prior behavior  |  New behavior
At 4 / 8 HP     |  At 4 / 8 HP
ooxx            |  ooxx
                |  
At 3 / 8 HP     |  At 3 / 8 HP
oxxx            |  ooxx
                |  
At 1 / 8 HP     |  At 1 / 8 HP
xxxx            |  oxxx
```