add librealsense2 dependency

Author: doronhi

realsense2_camera/package.xml

@@ -25,6 +25,7 @@
   <depend>tf</depend>
   <depend>ddynamic_reconfigure</depend>
   <depend>diagnostic_updater</depend>
+  <depend>librealsense2</depend>
   <export>
     <nodelet plugin="${prefix}/nodelet_plugins.xml" />
   </export>