`bundler_without_groups` should take precedence over automated config

The README states:

> When running Bundler, unnecessary groups will be skipped. The list of groups
> to skip is determined with this algorithm:
> 
> * start with this Array: development test cucumber staging production;
> * the group corresponding to the current environment will be removed from the
>   Array;
> * if the bundler_without_groups attribute is set, those groups will be added
>   to the Array.

yet, the current implementation prevented you from ignoring a group if it had
the same name as the current environment. This fixes that