Tweak Tmux's config.

A little more room for the session name.

.tmux.conf

 bind-key b send-prefix
 set -g set-titles on
 set -g set-titles-string '#T'
-set -g status-left-length 12
+set -g status-left-length 15
 
 # Copied from https://github.com/seebi/tmux-colors-solarized/blob/master/tmuxcolors-dark.conf
 #### COLOUR (Solarized dark)