Fix #94 start default-shell as login shell.
Fix #94 start default-shell as login shell.

If pane content is restored and no default-command is set, restore.sh
falls back to default-shell, which tmux sets automatically and calls as
a login shell.

In pane_creation_command() we need to make sure to call default-shell as a login shell.
As tmux does. But take care not to call default-command as a login shell.

tmux-plugins/tmux-resurrect