Update CHANGELOG.md for 10.3.8
Update CHANGELOG.md for 10.3.8

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