fix unit test fail on Travis
fix unit test fail on Travis

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