Merge pull request #5 from precariouspanther/phpunit-56-support

Add compatibility with PHPUnit 5.6^

Author: precariouspanther

composer.json

@@ -25,7 +25,7 @@
     "require": {
         "php": ">=5.6",
         "bigcommerce/injector": "@stable",
-        "phpunit/phpunit": "^6.0"
+        "phpunit/phpunit": "^6.0 || ^5.6"
     },
     "autoload": {
         "psr-4": {