fix open-streets-dc example syntax that I accidentally broke in e0f82b669dab06efcccc237f2363b8619c1c6e55 - closes #1639
fix open-streets-dc example syntax that I accidentally broke in e0f82b669dab06efcccc237f2363b8619c1c6e55 - closes #1639

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