remove windows and linux builds from travis, since we do those on circle now.
remove windows and linux builds from travis, since we do those on circle now.

paulmey/packer,bryson/packer,grubernaut/packer,tas50/packer,timsutton/packer,tas50/packer,timsutton/packer,tas50/packer,rnaveiras/packer,bryson/packer,mitchellh/packer,rnaveiras/packer,tas50/packer,rnaveiras/packer,grubernaut/packer,timsutton/packer,paulmey/packer,pecigonzalo/packer,dave2/packer,pecigonzalo/packer,paulmey/packer,mitchellh/packer,ricardclau/packer,rnaveiras/packer,bryson/packer,ricardclau/packer,mitchellh/packer,dave2/packer,grubernaut/packer,bryson/packer,pecigonzalo/packer,tas50/packer,hashicorp/packer,ricardclau/packer,bryson/packer,mitchellh/packer,timsutton/packer,paulmey/packer,timsutton/packer,grubernaut/packer,grubernaut/packer,dave2/packer,dave2/packer,ricardclau/packer,timsutton/packer,paulmey/packer,ricardclau/packer,grubernaut/packer,bryson/packer,dave2/packer,rnaveiras/packer,pecigonzalo/packer,paulmey/packer,dave2/packer,hashicorp/packer,rnaveiras/packer,mitchellh/packer,ricardclau/packer,hashicorp/packer,hashicorp/packer,tas50/packer