x11-drivers/xf86-input-libinput: Update to 0.30.0

Update x11-drivers/xf86-input-libinput to 0.30.0
This release implements scroll button lock, making it possible to configure
the scroll button on a mouse so that there is no need to hold it down while
scrolling.

Changelog:
https://lists.x.org/archives/xorg-announce/2020-May/003045.html