Fix a small typo in the delete merged branches documentation

doc/user/project/repository/branches/index.md

@@ -37,7 +37,7 @@ This feature allows merged branches to be deleted in bulk. Only branches that
 have been merged and [are not protected][protected] will be deleted as part of
 this operation.
 
-It's particularly useful to clean up old branches that were not deleting
+It's particularly useful to clean up old branches that were not deleted
 automatically when a merge request was merged.
 
 [ce-6449]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6449 "Add button to delete all merged branches"