[ci] Attempt to fix ipopt build for OSX#42

bchretien wants to merge 2 commits intoroboptim:masterroboptim/roboptim-core-plugin-ipopt:masterfrom

bchretien:fix/ci-osx-ipoptbchretien/roboptim-core-plugin-ipopt:fix/ci-osx-ipoptCopy head branch name to clipboard