Upgrade deps + change VAPID keys

Author: Minishlink

README.md

@@ -23,6 +23,9 @@ $ composer create-project minishlink/web-push-php-example
 $ cd web-push-php-example
 ```
 
+You can change the VAPID keys in the [keys](./keys) folder with [this guide](https://github.com/web-push-libs/web-push-php#authentication-vapid).
+Don't forget to update the public key in [app.js](./src/app.js) too.
+
 ## Usage
 
 ```bash

composer.json

@@ -10,6 +10,6 @@
         }
     ],
     "require": {
-        "minishlink/web-push": "^4.0"
+        "minishlink/web-push": "^4.0.0"
     }
 }