Update the Redis version required for Merge Trains

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

doc/ci/merge_request_pipelines/pipelines_for_merged_results/merge_trains/index.md

@@ -73,7 +73,7 @@ To enable merge trains:
 
 - You must have maintainer [permissions](../../../../user/permissions.md).
 - You must be using [GitLab Runner](https://gitlab.com/gitlab-org/gitlab-runner) 11.9 or later.
-- In GitLab 12.0 and later, you need [Redis](https://redis.io/) 3.2 or later.
+- In GitLab 13.0 and later, you need [Redis](https://redis.io/) 5.0 or later.
 - Your repository must be a GitLab repository, not an
   [external repository](../../../ci_cd_for_external_repos/index.md).