[CI] update doxygen to 1.8.15 on 14.04, ref #36
[CI] update doxygen to 1.8.15 on 14.04, ref #36

jmirabel/hpp-doc,humanoid-path-planner/hpp-doc,humanoid-path-planner/hpp-doc,florent-lamiraux/hpp-doc,florent-lamiraux/hpp-doc,jmirabel/hpp-doc