fixes #106 has function does not return true for directories

[MordiSacks]

[drionix]

Could also use this, since gcs interpret path name ending with slash ('/') as a directory.

public function has($path)
    {
        if ($this->getObject($path.'/')->exists()){
            return true;
	}
	return $this->getObject($path)->exists();
    }

Basically, this code check if the given path is a directory, if not, check if it is a file.