Forward CI env vars in Docker containers

[lyrixx]

list adapted from https://github.com/watson/ci-info/blob/master/index.js#L55-L58

>…ire/dev/github.com/jolicode/docker-starter(env *) inv test
Creating app_builder_run ... done
bool(false)
bool(false)

>…ire/dev/github.com/jolicode/docker-starter(env *) GITHUB_ACTIONS=12345 inv test
Creating app_builder_run ... done
string(5) "12345"
bool(false)

>…ire/dev/github.com/jolicode/docker-starter(env *) cat application/test.php
<?php

var_dump($_SERVER['GITHUB_ACTIONS'] ?? false);
var_dump($_SERVER['FOOBAR'] ?? false);

fixed #125