Add semver validation for version string.
Add semver validation for version string.

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