Update v3.13.0 release date

Author: timofurrer

CHANGELOG.md

@@ -8,9 +8,6 @@ FEATURES:
 * **New Resource**: `gitlab_project_environment` ([#938](https://github.com/gitlabhq/terraform-provider-gitlab/pull/938))
 * **New Resource**: `gitlab_project_protected_environment` ([#938](https://github.com/gitlabhq/terraform-provider-gitlab/pull/938))
 * **New Resource**: `gitlab_system_hook` ([#929](https://github.com/gitlabhq/terraform-provider-gitlab/pull/929))
-
-FEATURES:
-
 * resource/gitlab_topic: Support deletion ([#967](https://github.com/gitlabhq/terraform-provider-gitlab/pull/967))
 * resource/gitlab_topic: Support avatar images ([#968](https://github.com/gitlabhq/terraform-provider-gitlab/pull/968))
 * resource/gitlab_repository_file: Support using plain text `content` to beautify plans ([#972](https://github.com/gitlabhq/terraform-provider-gitlab/pull/972))