Add missing CHANGELOG.md entries for security release on 2017-01-23
The security release on Jan 23, 2017 that included versions v8.13.12
, v8.14.7
, and v8.15.5
is strangely absent from the CHANGELOG.md in gitlab-ce, however the entries do exist in the CHANGELOG.me for gitlab-ee. This MR restores these entries to the CHANGELOG for gitlab-ce.