replace :torso_lift_link to :torso_lift_link_lk for suppressing error in pr2-send-joints.l

Both 
```
(send *pr2* :links :torso_lift_link)
```
and
```
(send *pr2* :torso_lift_link_lk)
```
will do, but I don't know the difference of those.
I temporaly use the torso_lift_link_lk, if that is not correct, please change it to :links version