Update .travis.yml to test under PHP 7+

.travis.yml

@@ -1,16 +1,21 @@
 language: php
 
 php:
-  - 5.3
   - 5.4
   - 5.5
+  - 5.6
+  - 7.0
+  - 7.1
+  - 7.2
   - hhvm
 
 before_script:
   - wget http://getcomposer.org/composer.phar
   - php composer.phar install --dev
 
-script: phpunit --coverage-clover clover
+script:
+  - vendor/bin/phpunit --coverage-clover clover
+  - composer validate
 
 after_success:
   - curl -sL https://bit.ly/artifact-uploader | php

composer.json

@@ -2,7 +2,7 @@
     "name": "phpcollection/phpcollection",
     "description": "General-Purpose Collection Library for PHP",
     "keywords": ["collection", "list", "sequence", "map", "set"],
-    "license": "Apache2",
+    "license": "Apache-2.0",
     "authors": [
         {"name": "Johannes M. Schmitt", "email": "schmittjoh@gmail.com"}
     ],
@@ -18,5 +18,13 @@
         "branch-alias": {
             "dev-master": "0.4-dev"
         }
+    },
+    "require-dev": {
+        "phpunit/phpunit": "<6"
+    },
+    "config": {
+        "platform": {
+            "php": "5.4"
+        }
     }
 }