Fixed issue with validating decimals with Min/Max rules

The expected outcome of the below is ```true``` but was producing ```false```.

```php
$v = new Validator(array('num' => 0.9));
$v->rule('min', 'num', 0.5);
var_dump($v->validate()); // bool(false)
```

This was being caused by casting the ```$value``` to an ```int```.

```php
$x = (int) 0.9;
var_dump($x); // int(0)
```