[ticket/12141] Disable opcache on travis for php 5.5.8 aswell

PHPBB3-12141
Merge pull request #2017 from nickvergessen/ticket/12141

[ticket/12141] Disable opcache on travis for php 5.5.8 aswell

* nickvergessen/ticket/12141:
  [ticket/12141] Disable opcache on travis for php 5.5.8 aswell