Add queue_size keyword to Publisher

This solves the following issue:
```
/home/pal/reemc_indigo_ws/src/joy_teleop/scripts/joy_teleop.py:63: SyntaxWarning:
The publisher should be created with an explicit keyword argument 'queue_size'.
Please see http://wiki.ros.org/rospy/Overview/Publishers%20and%20Subscribers for more information.
  self.publishers[topic_name] = rospy.Publisher(topic_name, topic_type)
```
as reported by @awesomebytes