[ubuntu] How can I get a newer version of docker.io?

Hi,

I'm trying to use a newer argument in docker (docker.io):

It turns out that Ubuntu 15.10 has docker.io 1.6.2 as stable. It does not recognize the --build-arg argument.

I know that version 1.11 has this argument, but I don't know what version first gets it, as the older docs are not online.

Can somebody help out?

Thanks.