fix travis config

Author: matt-allan

.travis.yml

@@ -1,14 +1,10 @@
-dist: trusty
+dist: xenial
 language: php
 
 php:
   - 7.2
   - 7.3
-  - 7.4
-
-# This triggers builds to run on the new TravisCI infrastructure.
-# See: http://docs.travis-ci.com/user/workers/container-based-infrastructure/
-sudo: false
+  - 7.4snapshot
 
 ## Cache composer
 cache:
@@ -17,7 +13,7 @@ cache:
 
 matrix:
   include:
-    - php: 7.1
+    - php: 7.2
       env: 'COMPOSER_FLAGS="--prefer-stable --prefer-lowest"'
 
 before_script: