Travis: fix PHP 5.3 issue, add PHP 7.1

.travis.yml

 sudo: false
 
+dist: trusty
+
 language: php
 
 php:
-  - '5.3'
   - '5.4'
   - '5.5'
   - '5.6'
   - '7.0'
+  - '7.1'
+
+matrix:
+  include:
+    - php: '5.3'
+      dist: precise
 
 notifications:
   email: