keep-outdated should be keep-optional

[rdohms]

I'm struggling a bit with the concept of keep-outdated. While it does perfectly what i need it to do, it does seem to describe the wrong concept for me.

In my .dist.yml file i actually ommit 2 parameters which are optional, since they have default values defined in the config file, however, if i do not keep them in the dist file, this script removes them.

So in this case, they are not outdated parameters as much as they are optional parameters, i think that would be better naming for it, or at least better motivation to keep those around, as outdated, the concept, means no longer used.

Just thought it worth the discussion.