fixed the deployment button url

Author: JAXPARROW

README.md

@@ -10,7 +10,7 @@ These are sample clients for Facebook's [Webhooks](https://developers.facebook.c
 ### WhatsApp Cloud API Webhooks
 1. Deploy the sample app on Heroku with this button:
 
-    [![Deploy](https://www.herokucdn.com/deploy/button.svg)](https://github.com/JAXPARROW/whatsapi-flask-webhook)
+    [![Deploy](https://www.herokucdn.com/deploy/button.svg)](https://heroku.com/deploy?template=https://github.com/JAXPARROW/whatsapi-flask-webhook)
 
 
 1. Set up your client's [subscription] using your `https://<your-subdomain>.herokuapp.com/whatsapi` as the callback URL. It is recommended that you set a `TOKEN` and `APP_SECRET` [config var](https://devcenter.heroku.com/articles/config-vars) as part of the set up of your Heroku app to secure requests. If you choose not to set a config var, then you will need to set a verify token of 'token' when configuring the callback URL.