Merge pull request #9 from ghostwriter/feature/http-message-v2

Support `psr/http-message` v2

Author: Jean85

composer.json

@@ -20,7 +20,7 @@
     ],
     "require": {
         "php": ">=7.0",
-        "psr/http-message": "^1.0",
+        "psr/http-message": "^1.0 || ^2.0",
         "psr/http-server-handler": "^1.0"
     },
     "autoload": {