.travis.yml: re-enable hexane_ibi propane_ibi on ubuntu
.travis.yml: re-enable hexane_ibi propane_ibi on ubuntu

MrTheodor/csg,MrTheodor/csg,votca/csg,MrTheodor/csg,votca/csg,MrTheodor/csg,votca/csg,MrTheodor/csg,votca/csg