[ticket/12908] Fix operator typo in increment.php

PHPBB3-12908
Merge pull request #2792 from n-aleha/ticket/12908

[ticket/12908] Fix operator typo in increment.php

* n-aleha/ticket/12908:
  [ticket/12908] Fix operator typo in increment.php
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12908] Fix operator typo in increment.php