Getting error to make an upgrade to at least Gradle 6.8

Hi there,

I can only run your docker compose demo if I make some changes. Namely, the application port to 9081 in the docker-compose-desktop.yml (the application is configured to run on 9081 and not 9080 as it is) and the parent image to gradle:6.8.3-jdk-openj9. I tried to open a pull request for you, but I can't. Maybe I could fork the project, make the change and then make a pull request to you that way, but it think it's probably better to leave this to you, to keep it simple.

This is what I was getting:

Welcome to Gradle 5.4!

Here are the highlights of this release:
 - Run builds with JDK12
 - New API for Incremental Tasks
 - Updates to native projects, including Swift 5 support

For more details see https://docs.gradle.org/5.4/release-notes.html

Starting a Gradle Daemon (subsequent builds will be faster)

FAILURE: Build failed with an exception.

* Where:
Build file '/code/build.gradle' line: 15

* What went wrong:
A problem occurred evaluating root project 'code'.
> Failed to apply plugin [id 'org.springframework.boot']
   > Spring Boot plugin requires Gradle 6.8.x, 6.9.x, or 7.x. The current version is Gradle 5.4

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 6s
ERROR: Service 'app' failed to build: The command '/bin/sh -c gradle clean build -x test' returned a non-zero code: 1

It would be better to make this update in a way that people don't run into this in the future. Btw,, I think this is a great project! :+1:

resilience4j / resilience4j-spring-boot2-demo

Getting error to make an upgrade to at least Gradle 6.8 #58