update docs to use double quotes, which works on more shells (#11009)
update docs to use double quotes, which works on more shells (#11009)


hashicorp/packer,hashicorp/packer,mitchellh/packer,pecigonzalo/packer,hashicorp/packer,rnaveiras/packer,rnaveiras/packer,rnaveiras/packer,rnaveiras/packer,rnaveiras/packer,rnaveiras/packer,pecigonzalo/packer,pecigonzalo/packer,mitchellh/packer,hashicorp/packer,mitchellh/packer,mitchellh/packer,pecigonzalo/packer,mitchellh/packer