chore: drop PHP requirements from 7.3 to 7.2

Author: joostfaassen

composer.json

@@ -4,7 +4,7 @@
   "type": "library",
   "description": "Organization sync library",
   "require": {
-    "php": "^7.3",
+    "php": "^7.2",
     "doctrine/annotations": "^1.6",
     "knplabs/github-api": "^2.11",
     "php-http/guzzle6-adapter": "^1.1",