Increase queue_size in swri_roscpp/Subscriber.
Increase queue_size in swri_roscpp/Subscriber.

This commit increases the queue size for subscribers that use the
store mechanism instead of a callback.  The queue size was set to 1,
which we have seen problems with, so this will increase it to 2.

swri-robotics/marti_common,evenator/marti_common,evenator/marti_common,swri-robotics/marti_common,evenator/marti_common,swri-robotics/marti_common,elliotjo/marti_common,elliotjo/marti_common,swri-robotics/marti_common,elliotjo/marti_common,evenator/marti_common,elliotjo/marti_common