Update CHANGELOG.md for 9.1.9
Update CHANGELOG.md for 9.1.9

[ci skip]
jirutka/gitlabhq,jirutka/gitlabhq,dreampet/gitlab,iiet/iiet-git,dreampet/gitlab,dplarson/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,axilleas/gitlabhq,mmkassem/gitlabhq,t-zuehlsdorff/gitlabhq,t-zuehlsdorff/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,axilleas/gitlabhq,stoplightio/gitlabhq,dreampet/gitlab,iiet/iiet-git,axilleas/gitlabhq,t-zuehlsdorff/gitlabhq,t-zuehlsdorff/gitlabhq,iiet/iiet-git,dreampet/gitlab,stoplightio/gitlabhq,dplarson/gitlabhq,jirutka/gitlabhq,jirutka/gitlabhq,dplarson/gitlabhq,axilleas/gitlabhq,stoplightio/gitlabhq,dplarson/gitlabhq