[Cache] Update github link for method in Redis adapter

[MrYamous]

To reach the class where the method is implemented. It seems clearer to me WDYT ?

[javiereguiluz]

In this very same page, we have this:

.. note::

    See the :class:`Symfony\\Component\\Cache\\Traits\\RedisTrait` for more options
    you can pass as DSN parameters.

so, we're already linking to the RedisTrait and this proposal makes sense. Thanks Matthieu.