I was just adding tmux plugins to my .tmux.conf file to find out that one of the plugins (tmux-copycat I think) requires tmux 1.9. When I start tmux I get the message `Error: Tmux version unsupported. Please install tmux version 1.9 or greater!". So, what is the best way to upgrade tmux 1.8 to 1.9 on Ubuntu 14.04?