Rounding errors with Color.hsl().string()

Certain colors (I've only seen this in HSL so far) don't round correctly when calling `string()`.

For example:

```
var Color = require('color');

var pink = Color('#FF08C2');
console.log(pink.hsl().string()); // 'hsl(314.79999999999995, 100%, 51.6%)'
```