units of weight in inventory menu
pluralize

Rivet already fixed this but since nobody else is merging, I'll PR it.
Complying with the system FTW.
Merge branch 'fix-4-finger' of github.com:KA101/Cataclysm-DDA
Merge branch 'inv_weight_unit' of github.com:illi-kun/Cataclysm-DDA