Update CHANGELOG.md for 11.7.8

[ci skip]

CHANGELOG.md

@@ -562,6 +562,19 @@ entry.
 - Creates mixin to reduce code duplication between CE and EE in graph component.
 
 
+## 11.7.8 (2019-03-26)
+
+### Security (7 changes)
+
+- Disallow guest users from accessing Releases.
+- Fix PDF.js vulnerability.
+- Hide "related branches" when user does not have permission.
+- Fix XSS in resolve conflicts form.
+- Added rake task for removing EXIF data from existing uploads.
+- Disallow updating namespace when updating a project.
+- Use UntrustedRegexp for matching refs policy.
+
+
 ## 11.7.7 (2019-03-19)
 
 ### Security (2 changes)