Update MySQL docker-compose example

[maltewhiite]

Prerequisites

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Description

Update this example: https://github.com/teamatldocker/jira/blob/master/examples/mysql/docker-compose.yml

Afaik the latest version of Jira needs a higher MySQL version than 5.6.

Last commit was 2019.

[maltewhiite]

This example uses a higher compose version, and contains more details: https://github.com/teamatldocker/jira/blob/master/docker-compose.yml