fix invalid range error on grep

`rosrun robot_upstart install turtlebot_bringup/launch/minimal.launch --interface wlan0` described in http://wiki.ros.org/robot_upstart did not work due to http://stackoverflow.com/questions/26754181/greps-invalid-range-end-bug-or-feature
```
If you want to match the character -, among others, just add it in the edges of the expression: as the first or last item.
```