Enable yank-last-arg for Vi binding

[amitkot]

yank-last-arg was enabled for Emacs binding as part of #343.
It would be very useful to have it enabled for Vi binding as well.

I'm using Xonsh and as a workaround for the time being I am using this binding:

@events.on_ptk_create
def custom_keybindings(bindings, **kw):

    @bindings.add('escape', '.')
    def yank_last(event):
        event.current_buffer.yank_last_arg()