Update phpunit/phpunit requirement from 7.4.* || 8.3.* to 7.4.* |… (#10)

Update phpunit/phpunit requirement from 7.4.* || 8.3.* to 7.4.* || 8.3.* || 8.4.*

Author: Kevin Buchholz

composer.json

@@ -32,7 +32,7 @@
         "consistence/coding-standard": "3.7",
         "orchestra/testbench": "~3.0 || 4.*",
         "phpmd/phpmd": "^2.6",
-        "phpunit/phpunit": "7.4.* || 8.3.*",
+        "phpunit/phpunit": "7.4.* || 8.3.* || 8.4.*",
         "slevomat/coding-standard": "4.8.7",
         "squizlabs/php_codesniffer": "^3.4"
     },