[UX] naturallightwidget: Use unicode minus for button
[UX] naturallightwidget: Use unicode minus for button

lgeek/koreader,koreader/koreader,koreader/koreader,NiLuJe/koreader,mihailim/koreader,mwoz123/koreader,Frenzie/koreader,Markismus/koreader,Hzj-jie/koreader,NiLuJe/koreader,houqp/koreader,poire-z/koreader,Frenzie/koreader,poire-z/koreader,pazos/koreader