Update composer configs to set platformat php 7.4.

This has been tested on newer versions of PHP and found to be working however due to other library constraints composer will not install packages without the added platform config.

Author: chrisryan

composer.json

@@ -16,6 +16,9 @@
     ],
     "license": "MIT",
     "config": {
+        "platform": {
+            "php": "7.4"
+        },
         "sort-packages": true,
         "allow-plugins": {
             "php-http/discovery": true