Add self-update command

Author: bennothommo

composer.json

@@ -11,7 +11,9 @@
     ],
     "require": {
         "php": ">=7.2",
-        "symfony/console": "^4.4.13"
+        "symfony/console": "^4.4.13",
+        "php-http/guzzle6-adapter": "^2.0",
+        "knplabs/github-api": "^2.15"
     },
     "require-dev": {
         "bamarni/composer-bin-plugin": "^1.4"