chore: adds support for 8.1 on CI (#217)

Author: jcchavezs

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
       fail-fast: false
       matrix:
         operating-system: [ubuntu-latest, windows-latest, macos-latest]
-        php-versions: ["7.4", "8.0"]
+        php-versions: ["7.4", "8.0", "8.1"]
     steps:
       - name: Checkout
         uses: actions/checkout@v2