[ticket/13085] Fix typo in oauth.php

PHPBB3-13085
Merge pull request #2976 from n-aleha/ticket/13085

[ticket/13085] Fix typo in oauth.php
Merge branch 'develop-ascraeus' into develop

# By n-aleha
# Via Dhruv Goel (1) and n-aleha (1)
* develop-ascraeus:
  [ticket/13085] Fix typo in oauth.php