Retrieve the user's email addresses regardless if their status is set public or not

Update GithubOAuth.php

The /user API returns only the data the user explicitly set as public and null for those he didn't. 

If the user did not set the email address public (me for example), the email address being mandatory for the process, the authentication fails returning an error message.

By using the /user/emails API in conjunction, it is possible to retrieve all the email addresses the user set in Github, regardless if they are set public or not, and select one of those (ex: primary one), for the login process to complete successfully.

…-Github

Retrieve mandatory email address from Github