Constructor
new BubbleHealth(game, startX, startY, id, value)
    Create a health bubble.
    Parameters:
| Name | Type | Description | 
|---|---|---|
| game | SpaceInvaders | The current game. | 
| startX | number | Starting X position. | 
| startY | number | Starting Y position. | 
| id | string | Unique HTML DOM id. | 
| value | number | Value displayed in the bubble. | 
- Source:
Extends
Methods
move() → {boolean}
    Move the bubble up or down based on direction.
Collision detection on screen edges.
- Inherited From:
- Source:
Returns:
- Type
- boolean
update() → {boolean}
    Update the bubble, call move and fade it out. 
When faded out disable it. BubbleFactory will kill it
on the next update.
- Inherited From:
- Source:
Returns:
- Type
- boolean