Missed required settings by rfc which genereates PHP Notice

The AOuth spec requires client_id and client_secret and the PHP library used by Sugar check both of these variables in file vendor/oauth2-php/lib/OAuth2.php on line 774. The current result without this setting is a PHP notice on Sugar instance "PHP Notice:  Undefined index: client_secret"
Merge pull request #21 from cmourizard/patch-2

Missed required settings by rfc which genereates PHP Notice