added different coloured balls and random generator

added some different colored balls to show user enemy vs balls you can eat.
I think you could accomplish this with something more like
```js
var enemySpriteNames = ['blue_ball', 'red_ball', 'green_ball'];
var spriteName = enemySpriteNames[Math.floor(Math.random() * enemySpriteNames.length)];
var enemy = smallerEnemies.create(game.world.randomX, game.world.randomY, spriteName);
```
...or combine the latter two lines.

Or, since you're using Phaser, use `game.rnd.pick`:
```js
var enemySpriteNames = ['blue_ball', 'red_ball', 'green_ball'];
var enemy = smallerEnemies.create(game.world.randomX, game.world.randomY, game.rnd.pick(enemySpriteNames));
```