Tag jessie images

[mcandre]

Please tag any Docker images that base from Jessie, just as ya tag images that base from Wheezy and Alpine. I think the simple "golang:1.8" tag happens to use Jessie, but just in case that changes, it would be nice to have a more specific tag for choosy system administrators.

[tianon]

Good idea! 👍

(see #170 😄)