Battery subsystem causes fatal error on Kobo Libra 2

[ticky]

On my Kobo Libra 2, Plato 0.9.27 fails to start, and I get the following in info.log:

Error: can't build context

Caused by:
    0: can't create battery
    1: No such file or directory (os error 2)

This appears to be down to an oversight in the battery reading code; as a Mark 9 device, the Libra 2 exposes the battery device at /sys/class/power_supply/battery, not /sys/class/power_supply/mc13892_bat, but the battery code is treating it as if it were an earlier device:

plato/src/battery/kobo.rs

Line 34 in 0f7fdea

let base = if CURRENT_DEVICE.mark() != 8 {

I believe this could be fixed by merging #185, or by changing the above line to < instead of !=