GitHub Actions - added PHP 8.0 and 8.1 (#12)

Author: grogy

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       max-parallel: 10
       matrix:
-        php: [ '7.3', '7.4']
+        php: [ '7.3', '7.4', '8.0', '8.1']
 
     steps:
       - name: Set up PHP