Remove Ubuntu Vivid (EOL)

https://lists.ubuntu.com/archives/ubuntu-announce/2016-February/000204.html

library/ubuntu

@@ -8,7 +8,6 @@
 #  - e406914 Update tarballs
 #    - `ubuntu:precise`: 20160108
 #    - `ubuntu:trusty`: 20160119
-#    - `ubuntu:vivid`: 20160122
 #    - `ubuntu:wily`: 20160121
 #    - `ubuntu:xenial`: 20160125
 
@@ -25,11 +24,6 @@ trusty-20160119: git://github.com/tianon/docker-brew-ubuntu-core@e406914e5f64800
 trusty: git://github.com/tianon/docker-brew-ubuntu-core@e406914e5f648003dfe8329b512c30c9ad0d2f9c trusty
 latest: git://github.com/tianon/docker-brew-ubuntu-core@e406914e5f648003dfe8329b512c30c9ad0d2f9c trusty
 
-# 20160122
-15.04: git://github.com/tianon/docker-brew-ubuntu-core@e406914e5f648003dfe8329b512c30c9ad0d2f9c vivid
-vivid-20160122: git://github.com/tianon/docker-brew-ubuntu-core@e406914e5f648003dfe8329b512c30c9ad0d2f9c vivid
-vivid: git://github.com/tianon/docker-brew-ubuntu-core@e406914e5f648003dfe8329b512c30c9ad0d2f9c vivid
-
 # 20160121
 15.10: git://github.com/tianon/docker-brew-ubuntu-core@e406914e5f648003dfe8329b512c30c9ad0d2f9c wily
 wily-20160121: git://github.com/tianon/docker-brew-ubuntu-core@e406914e5f648003dfe8329b512c30c9ad0d2f9c wily