fix:
[ 80%] Building CXX object tests/CMakeFiles/romeo-small.dir/romeo-small.cc.o
In file included from /workspace/src/hpp-wholebody-step/include/hpp/wholebody-step/fwd.hh:24:0,
                 from /workspace/src/hpp-wholebody-step/include/hpp/wholebody-step/static-stability-constraint.hh:23,
                 from /workspace/src/hpp-wholebody-step/tests/romeo-small.cc:35:
/workspace/install/include/hpp/walkgen/fwd.hh:25:39: fatal error: roboptim/trajectory/fwd.hh: No such file or directory

when roboptim is installed from robotpkg,
ref https://github.com/humanoid-path-planner/hpp-doc/issues/23