Update CHANGELOG.md for 11.9.8

[ci skip]

CHANGELOG.md

@@ -2,6 +2,22 @@
 documentation](doc/development/changelog.md) for instructions on adding your own
 entry.
 
+## 11.9.8 (2019-04-11)
+
+### Deprecated (1 change)
+
+- Allow to use untrusted Regexp via feature flag. !26905
+
+### Performance (2 changes)
+
+- Improve performance of PR import. !27121
+- Disable method instrumentation for diffs. !27235
+
+### Other (1 change)
+
+- Restore HipChat project service. !27172
+
+
 ## 11.9.7 (2019-04-09)
 
 - No changes.

changelogs/unreleased/allow-to-use-untrusted-ruby-syntax.yml

----
-title: Allow to use untrusted Regexp via feature flag
-merge_request: 26905
-author:
-type: deprecated

changelogs/unreleased/fix-pull-request-importer.yml

----
-title: Improve performance of PR import
-merge_request: 27121
-author:
-type: performance

changelogs/unreleased/restore-hipchat.yml

----
-title: Restore HipChat project service
-merge_request: 27172
-author:
-type: change

changelogs/unreleased/sh-disable-diff-instrumentation.yml

----
-title: Disable method instrumentation for diffs
-merge_request: 27235
-author:
-type: performance