Point script at correct rqt binary.

When using the current version of turtlebot_dashboard I get the following error:

    ~/ros_groovy$ rosrun turtlebot_dashboard turtlebot_dashboard
    [rosrun] Couldn't find executable named rqt below /opt/ros/groovy/share/rqt_gui

I do see the rqt binary in /opt/ros/groovy/bin, but rosrun seems to require running rqt_gui binary instead.