The `docker-compose` setup uses features that
are not available in all versions. This pins
the `docker-compose` setup to version `3.4`
instead of just `3`.

It is known to work under the following versions:

```
$ uname -or
5.10.70-1-MANJARO GNU/Linux

$ docker-compose --version
Docker Compose version 2.0.1

$ docker --version
Docker version 20.10.9, build c2ea9bc90b
```