test with php 5.6

Author: streamtw

.travis.yml

@@ -1,14 +1,15 @@
 language: php
 
 php:
-  - 7.0
-  - 7.1
   - 7.2
+  - 7.1
+  - 7.0
+  - 5.6
 
 matrix:
   fast_finish: true
   allow_failures:
-    - php: 7.0
+    - php: 5.6
 
 before_script:
   - travis_retry composer self-update