Merge pull request #77 from php-http/php-81

build with php 8.1

Author: dbu

.github/workflows/Build-Test.yml

@@ -13,7 +13,7 @@ jobs:
       fail-fast: false
       matrix:
         operating-system: [ubuntu-20.04]
-        php-versions: ['7.2', '7.3', '7.4', '8.0']
+        php-versions: ['7.2', '7.3', '7.4', '8.0', '8.1']
         include:
           - operating-system: ubuntu-16.04
             php-versions: '7.1'