fix typo

This was fixed in the upstream project in this commit. https://github.com/fkooman/php-oauth-client/commit/5499f0aad493bf863a3abc6ff2fc1a19277fa54f

Not sure why we decided to maintain our own fork but since we have diverged from the main project... let the maintenance begin.

@Kdub91712 Please review.
@ajayanty When this is approved and merged, please create the tag `1.1.3`. Thanks.