check for dvipng in test
check for dvipng in test

hssm/anki,florianjacob/anki,abeyer/anki,weihautin/anki,jakesyl/ruby-card,jkitching/anki,sunclx/anki,xuewenfei/anki,weihautin/anki,LucasCabello/anki,socialpercon/anki-1,go38/anki,hssm/anki,ospalh/libanki3,Stvad/anki,holycrepe/anki,kenjhim/anki,Arthaey/anki,subfusc/anki,eduOS/anki,jakesyl/ruby-card