currently, the key-handler will not receive the `S-` modifier if there's
a capital equivalent of that KEY.
if https://github.com/nsxiv/nsxiv/pull/78 is to be merged, then this
behaviour may change.
however as it currently stands, we should fix the comment. we can update
it later if needed.
Co-authored-by: Berke Kocaoğlu <berke.kocaoglu@metu.edu.tr>