Update MySQL docker-compose example

[maltewhiite]

Prerequisites

• [x] Put an X between the brackets on this line if you have done all of the following:
  • Reproduced the problem.
  • Checked that your issue isn't already filed.
  • Filled the form.
  • Included logs and system information.

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