rviz is using deprecated tinyxml interface of URDF

[wjwwood]

It produces a warning like this in melodic:

[ 81%] Building CXX object src/rviz/default_plugin/CMakeFiles/rviz_default_plugin.dir/robot_model_display.cpp.o
/home/william/melodic/src/rviz/src/rviz/default_plugin/robot_model_display.cpp: In member function ‘virtual void rviz::RobotModelDisplay::load()’:
/home/william/melodic/src/rviz/src/rviz/default_plugin/robot_model_display.cpp:185:41: warning: ‘bool urdf::Model::initXml(TiXmlElement*)’ is deprecated: TinyXML API is deprecated, use the TinyXML2 version instead [-Wdeprecated-declarations]
   if( !descr.initXml( doc.RootElement() ))
                                         ^
In file included from /home/william/melodic/src/rviz/src/rviz/default_plugin/robot_model_display.cpp:34:0:
/home/william/melodic/install/include/urdf/model.h:61:99: note: declared here
   URDF_EXPORT URDF_DEPRECATED("TinyXML API is deprecated, use the TinyXML2 version instead") bool initXml(TiXmlElement * xml);
                                                                                                   ^~~~~~~