Use consistent syntax for tmux mappings

`bind` is effectively an alias for `bind-key`:

See https://superuser.com/questions/581939/on-tmux-what-is-the-difference-between-bind-and-bind-key

tmux.conf

@@ -3,10 +3,10 @@ set -g default-terminal 'screen-256color'
 
 # act like vim
 setw -g mode-keys vi
-bind h select-pane -L
-bind j select-pane -D
-bind k select-pane -U
-bind l select-pane -R
+bind-key h select-pane -L
+bind-key j select-pane -D
+bind-key k select-pane -U
+bind-key l select-pane -R
 bind-key -r C-h select-window -t :-
 bind-key -r C-l select-window -t :+