Add support for phpunit 8.0

Ref: #261

Signed-off-by: William Desportes <williamdes@wdes.fr>

Author: williamdes

.gitignore

@@ -9,3 +9,4 @@ coverage.xml
 *sw[op]
 phpunit.xml
 phpcs.xml
+/.phpunit.result.cache

composer.json

@@ -22,7 +22,7 @@
     "require-dev": {
         "sami/sami": "^4.0",
         "phpunit/php-code-coverage": "*",
-        "phpunit/phpunit": "^7.4",
+        "phpunit/phpunit": "^7.4 || ^8.0",
         "phpmyadmin/coding-standard": "^1.0"
     },
     "conflict": {