Test php 8

Author: casperbakker

.github/workflows/phpunit.yml

@@ -9,7 +9,7 @@ jobs:
 
     strategy:
       matrix:
-        php-versions: ['7.2', '7.3', '7.4']
+        php-versions: ['7.2', '7.3', '7.4', '8.0']
 
     steps:
     - uses: actions/checkout@v2