Travis test against new 3.1.x branch name

Author: iMattPro

.travis.yml

@@ -32,7 +32,7 @@ env:
     - SNIFF="1"        # Should we run code sniffer on your code?
     - IMAGE_ICC="1"    # Should we run icc profile sniffer on your images?
     - EPV="1"          # Should we run EPV (Extension Pre Validator) on your code?
-    - PHPBB_BRANCH="develop-ascraeus"
+    - PHPBB_BRANCH="3.1.x"
 
 branches:
   only: