[Makefile] Use master branches of roboptim
[Makefile] Use master branches of roboptim

  - roboptim-core and roboptim-trajectory were using version-3.1.

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