disable mapnik 3.x testing until PPA is fixed
disable mapnik 3.x testing until PPA is fixed

nyimbi/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,Zhao-Qi/tilemill,nyimbi/tilemill,MappingKat/tilemill,MappingKat/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,florianf/tileoven,florianf/tileoven,Teino1978-Corp/Teino1978-Corp-tilemill,fxtentacle/tilemill,fxtentacle/tilemill,Zhao-Qi/tilemill,tilemill-project/tilemill,nyimbi/tilemill,paulovieira/tilemill-clima,MappingKat/tilemill,tilemill-project/tilemill,nyimbi/tilemill,Zhao-Qi/tilemill,tizzybec/tilemill,mbrukman/tilemill,MappingKat/tilemill,paulovieira/tilemill-clima,tilemill-project/tilemill,mbrukman/tilemill,nyimbi/tilemill,MappingKat/tilemill,Zhao-Qi/tilemill,fxtentacle/tilemill,fxtentacle/tilemill,tizzybec/tilemill,paulovieira/tilemill-clima,mbrukman/tilemill,fxtentacle/tilemill,tizzybec/tilemill,tizzybec/tilemill,mbrukman/tilemill,paulovieira/tilemill-clima,paulovieira/tilemill-clima,Teino1978-Corp/Teino1978-Corp-tilemill,tizzybec/tilemill,Zhao-Qi/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,mbrukman/tilemill,florianf/tileoven