Update docs for Redis with the minimum version 5.0

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

README.md

@@ -81,7 +81,7 @@ GitLab is a Ruby on Rails application that runs on the following software:
 - Ubuntu/Debian/CentOS/RHEL/OpenSUSE
 - Ruby (MRI) 2.7.2
 - Git 2.31+
-- Redis 4.0+
+- Redis 5.0+
 - PostgreSQL 11+
 For more information please see the [architecture](https://docs.gitlab.com/ee/development/architecture.html) and [requirements](https://docs.gitlab.com/ee/install/requirements.html) documentation.