Travis apparently changed its behavior.

gn36 · gn36 · commit 2112c2a48c70 · 2015-04-12T02:05:11.000+02:00
There is sudo in the phpbb standard setup commands.
diff --git a/.travis.yml b/.travis.yml
@@ -1,4 +1,5 @@
 language: php
+sudo: required
 
 matrix:
   include:
