Garbage collection is never executed resulting in GB's of CSS and JS files

In the GarbageCollector class garbage collection is executed when 

``` php
get_option( self::$code, 0 ) <= time() - $this->offset
```

However `self::$code` is always updated resulting in the GarbageCollector never actually doing the necessary cleanup.

``` php
update_option( self::$code, time() );
```
