Added PHP 8.0 to composer.json

Author: Sébastien Lévêque

composer.json

@@ -15,12 +15,11 @@
         "sort-packages": true
     },
     "require": {
-        "php": "^7.1",
+        "php": "^5.4|^7.0|^8.0"
         "psr/http-message": "^1.0",
         "php-http/client-implementation": "^1.0",
         "php-http/httplug": "^1.0",
         "php-http/discovery": "^1.0",
-
         "php-http/message": "^1.0"
     },
     "require-dev": {