Merge pull request #1289 from tianon/ubuntu-xenial

Finally add "ubuntu:xenial"

library/ubuntu

@@ -10,6 +10,8 @@
 #    - `ubuntu:trusty`: 20151208
 #    - `ubuntu:vivid`: 20151208
 #    - `ubuntu:wily`: 20151208
+#  - 8af9ba3 Update tarballs
+#    - `ubuntu:xenial`: 20151218.1
 
 # 20151208
 12.04.5: git://github.com/tianon/docker-brew-ubuntu-core@3852ef7c7e841ea8c126c9b00e64eeca61fe5ab0 precise
@@ -33,3 +35,8 @@ vivid: git://github.com/tianon/docker-brew-ubuntu-core@3852ef7c7e841ea8c126c9b00
 15.10: git://github.com/tianon/docker-brew-ubuntu-core@3852ef7c7e841ea8c126c9b00e64eeca61fe5ab0 wily
 wily-20151208: git://github.com/tianon/docker-brew-ubuntu-core@3852ef7c7e841ea8c126c9b00e64eeca61fe5ab0 wily
 wily: git://github.com/tianon/docker-brew-ubuntu-core@3852ef7c7e841ea8c126c9b00e64eeca61fe5ab0 wily
+
+# 20151218.1
+16.04: git://github.com/tianon/docker-brew-ubuntu-core@8af9ba31ba5d204717f9aff66c9c033454d72ba5 xenial
+xenial-20151218.1: git://github.com/tianon/docker-brew-ubuntu-core@8af9ba31ba5d204717f9aff66c9c033454d72ba5 xenial
+xenial: git://github.com/tianon/docker-brew-ubuntu-core@8af9ba31ba5d204717f9aff66c9c033454d72ba5 xenial