Allow PHP 8 (declarative composer.json change); remove platform config

Author: someniatko

composer.json

@@ -3,7 +3,7 @@
     "description": "Simple PSR-15 middleware for decoding JSON body of a server request when given respective Content-Type header",
     "type": "library",
     "require": {
-        "php": "^7.3",
+        "php": "^7.3 || ^8.0",
         "ext-json": "*",
         "psr/http-message": "^1.0",
         "psr/http-server-middleware": "^1.0",
@@ -23,10 +23,5 @@
             "Test\\": "test"
         }
     },
-    "config": {
-        "platform": {
-            "php": "7.3.0"
-        }
-    },
     "license": "MIT"
 }