Drop support for php 5.4 and 5.5

Add travis for php 7.1

Author: Cliff Odijk

.travis.yml

@@ -1,13 +1,14 @@
 language: php
 
 php:
-  - 5.4
-  - 5.5
   - 5.6
   - 7.0
+  - 7.1
 
 before_script:
-  - composer selfupdate
+  - composer self-update
+
+install:
   - composer install --prefer-dist
 
 script:

composer.json

@@ -17,7 +17,7 @@
         }
     ],
     "require": {
-        "php": ">=5.4",
+        "php": "^5.6 || ^7.0",
         "beberlei/assert": "~2.0"
     },
     "require-dev": {