Introduced also php-unit 8.x in require dev and updated images for ci

Author: giovannialbero1992

.ci/packer_cache.sh

@@ -2,10 +2,11 @@
 
 source /usr/local/bin/bash_standard_lib.sh
 
-DOCKER_IMAGES="8.0.0beta3-cli-buster
+DOCKER_IMAGES="php:8.0.0rc1-cli-buster
 php:7.4-cli
 php:7.3-cli
 php:7.2-cli
+php:7.1-cli
 "
 
 for di in ${DOCKER_IMAGES}

composer.json

@@ -23,7 +23,7 @@
     "doctrine/inflector": "^1.3",
     "mockery/mockery": "^1.2",
     "phpstan/phpstan": "^0.12",
-    "phpunit/phpunit": "^7.5 || ^9.3",
+    "phpunit/phpunit": "^7.5 || ^8.5 || ^9.3",
     "squizlabs/php_codesniffer": "^3.4",
     "symfony/finder": "~4.0",
     "symfony/yaml": "~4.0"