chore: bump minimum PHP version to 8.1

Author: evansims

README.md

@@ -6,7 +6,7 @@ This library inherits [psr-mock/http-message-implementation](https://github.com/
 
 ## Requirements
 
--   PHP 8.0+
+-   PHP 8.1+
 
 ## Installation
 

composer.json

@@ -19,7 +19,7 @@
     ],
     "homepage": "https://github.com/psr-mock/http-factory-implementation",
     "require": {
-        "php": "^8.0",
+        "php": "^8.1",
         "psr/http-factory": "^1.0",
         "psr/http-message": "^1.0",
         "psr-mock/http-message-implementation": "^1.0"