[tmux] Handle version 1.9a

Need to regex check for the version match instead of looking for exactly
version 1.9.

tmux/.tmux.conf

@@ -90,7 +90,7 @@ bind -r - resize-pane -D 3
 bind -r + resize-pane -U 3
 bind -r = resize-pane -U 3
 
-if-shell "[[ `tmux -V` == *1.9 ]]" \
+if-shell "[[ `tmux -V` =~ '1.9' ]]" \
   "set-option -g renumber-windows on; \
    bind c new-window -c '#{pane_current_path}'; \
    bind C-c new-window -c '#{pane_current_path}'; \