Add missing dependency to effort_controllers (#1531)

Author: urfeex

ur_robot_driver/package.xml

@@ -47,6 +47,7 @@
   <depend>ur_description</depend>
   <depend>ur_msgs</depend>
 
+  <exec_depend>effort_controllers</exec_depend>
   <exec_depend>force_torque_sensor_broadcaster</exec_depend>
   <exec_depend>joint_state_broadcaster</exec_depend>
   <exec_depend>joint_state_publisher</exec_depend>