fix missing comma in docs for lxd builder
fix missing comma in docs for lxd builder

timsutton/packer,ricardclau/packer,ChrisLundquist/packer,ChrisLundquist/packer,bryson/packer,mitchellh/packer,youhong316/packer,timsutton/packer,tb3088/packer,pecigonzalo/packer,grubernaut/packer,tas50/packer,grubernaut/packer,hashicorp/packer,tb3088/packer,paulmey/packer,tb3088/packer,ricardclau/packer,tas50/packer,bryson/packer,ricardclau/packer,youhong316/packer,KohlsTechnology/packer,youhong316/packer,paulmey/packer,tas50/packer,dave2/packer,rnaveiras/packer,youhong316/packer,bryson/packer,youhong316/packer,tas50/packer,rnaveiras/packer,KohlsTechnology/packer,dave2/packer,tb3088/packer,KohlsTechnology/packer,timsutton/packer,ricardclau/packer,dave2/packer,bryson/packer,bryson/packer,tb3088/packer,ChrisLundquist/packer,mkuzmin/packer,dave2/packer,dave2/packer,mitchellh/packer,bryson/packer,tb3088/packer,grubernaut/packer,mitchellh/packer,rnaveiras/packer,pecigonzalo/packer,paulmey/packer,KohlsTechnology/packer,ricardclau/packer,mkuzmin/packer,hashicorp/packer,timsutton/packer,mkuzmin/packer,mitchellh/packer,grubernaut/packer,tas50/packer,ricardclau/packer,rnaveiras/packer,mitchellh/packer,ChrisLundquist/packer,pecigonzalo/packer,paulmey/packer,ChrisLundquist/packer,paulmey/packer,mkuzmin/packer,tas50/packer,dave2/packer,rnaveiras/packer,mkuzmin/packer,rnaveiras/packer,grubernaut/packer,grubernaut/packer,hashicorp/packer,KohlsTechnology/packer,paulmey/packer,mkuzmin/packer,timsutton/packer,timsutton/packer,KohlsTechnology/packer,pecigonzalo/packer,ChrisLundquist/packer,youhong316/packer,hashicorp/packer