install luajit for luacov in Travis
install luajit for luacov in Travis

mihailim/koreader,NiLuJe/koreader,Hzj-jie/koreader,NickSavage/koreader,koreader/koreader,ashhher3/koreader,apletnev/koreader,houqp/koreader,Frenzie/koreader,Markismus/koreader,robert00s/koreader,ashang/koreader,noname007/koreader,chrox/koreader,poire-z/koreader,frankyifei/koreader,mwoz123/koreader,lgeek/koreader,NiLuJe/koreader,pazos/koreader,chihyang/koreader,Frenzie/koreader,koreader/koreader,poire-z/koreader