Update CHANGELOG.md for 10.2.6

[ci skip]

CHANGELOG.md

@@ -193,6 +193,21 @@ entry.
 - Clean up schema of the "merge_requests" table.
+## 10.2.6 (2018-01-11)
+
+### Security (9 changes, 1 of them is from the community)
+
+- Fix writable shared deploy keys.
+- Filter out sensitive fields from the project services API. (Robert Schilling)
+- Fix RCE via project import mechanism.
+- Fixed IPython notebook output not being sanitized.
+- Prevent OAuth login POST requests when a provider has been disabled.
+- Prevent a SQL injection in the MilestonesFinder.
+- Check user authorization for source and target projects when creating a merge request.
+- Fix path traversal in gitlab-ci.yml cache:key.
+- Fix XSS vulnerability in pipeline job trace.
+
+
 ## 10.2.5 (2017-12-15)
 ### Fixed (8 changes)