Update README.rst

fix url to api key

Author: Kien Pham

README.rst

@@ -72,7 +72,7 @@ encouraged to set ``raise_errors`` to ``True`` for forwards compatibility.
 Usage
 ~~~~~
 
-To begin using this library create a new instance of `SendGridClient` with your SendGrid credentials or a SendGrid API Key. API Key is the preferred method. API Keys are in beta. To configure API keys, visit https://sendgrid.com/beta/settings/api_key.
+To begin using this library create a new instance of `SendGridClient` with your SendGrid credentials or a SendGrid API Key. API Key is the preferred method. API Keys are in beta. To configure API keys, visit https://app.sendgrid.com/settings/api_keys.
 
 .. code:: python