Silent warnings

Explicitly cast `joints`/`links` size to avoid compilation warnings:

```
/home/dell/ros_fanuc_ws/src/industrial_core/industrial_utils/src/utils.cpp: In function ‘bool industrial_utils::findChainJointNames(const boost::shared_ptr<const urdf::Link>&, bool, std::vector<std::basic_string<char> >&)’:
/home/dell/ros_fanuc_ws/src/industrial_core/industrial_utils/src/utils.cpp:81:1117: warning: format ‘%d’ expects argument of type ‘int’, but argument 8 has type ‘std::vector<boost::shared_ptr<urdf::Joint> >::size_type {aka long unsigned int}’ [-Wformat=]
   ROS_DEBUG("Found %d child joints:", joints.size());                                                                                                                                                                                                                                                                                                                                                                         ^
/home/dell/ros_fanuc_ws/src/industrial_core/industrial_utils/src/utils.cpp:103:1116: warning: format ‘%d’ expects argument of type ‘int’, but argument 8 has type ‘std::vector<boost::shared_ptr<urdf::Link> >::size_type {aka long unsigned int}’ [-Wformat=]
   ROS_DEBUG("Found %d child links:", links.size());

```
Is the typecast still necessary with the `%lu` format specifier?