Merge pull request #19 from scotteh/dependabot/composer/phpunit/phpunit-tw-7.0or-tw-8.0

Update phpunit/phpunit requirement from ^7.0 to ^7.0 || ^8.0

Author: Andrew Scott

composer.json

@@ -19,7 +19,7 @@
         "symfony/css-selector": "^4.0 || ^5.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^7.0",
+        "phpunit/phpunit": "^7.0 || ^8.0",
         "phpdocumentor/phpdocumentor": "^2.9"
     },
     "autoload": {