Merge pull request #7 from formatz/master

Allow psr/http-message 2.0

Author: loevgaard

composer.json

@@ -16,7 +16,7 @@
         "facebook/php-business-sdk": "^14.0",
         "psr/http-client": "^1.0",
         "psr/http-factory": "^1.0",
-        "psr/http-message": "^1.0",
+        "psr/http-message": "^1.0 || ^2.0",
         "psr/log": "^1.1 || ^2.0 || ^3.0",
         "webmozart/assert": "^1.11"
     },