Fix typo

Author: romainneutron

UPGRADE-3.0.md

@@ -13,7 +13,7 @@
     * `Github\HttpClient\Plugin\History`
     * `Github\HttpClient\Plugin\PathPrepend`
 
-### Authetication methods
+### Authentication methods
 
 * `Github\Client::AUTH_URL_TOKEN` use `Github\Client::AUTH_ACCESS_TOKEN` instead.
 * `Github\Client::AUTH_URL_CLIENT_ID` use `Github\Client::AUTH_CLIENT_ID` instead.