Unprepared method returns opposite of what's expected

[bricehartmann]

https://github.com/tareq1988/wp-eloquent/blob/master/src/Eloquent/Database.php#L309

Currently the unprepared method will return true if an error occurs and false if an error does not occur.

I believe this should be something like:

return ($result !== false && empty($this->wpdb->last_error));