postprocess: we need to open the file as enc=utf8 on windows py3
postprocess: we need to open the file as enc=utf8 on windows py3

fixes #521

dalgr/svtplay-dl,dalgr/svtplay-dl,selepo/svtplay-dl,iwconfig/svtplay-dl,iwconfig/svtplay-dl,spaam/svtplay-dl,qnorsten/svtplay-dl,olof/svtplay-dl,selepo/svtplay-dl,qnorsten/svtplay-dl,olof/svtplay-dl,spaam/svtplay-dl