Update dependencies

- removed old versions of PHP
- updated PHPUnit to the latest version

Author: buskamuza

composer.json

@@ -8,12 +8,12 @@
     "AFL-3.0"
   ],
   "require": {
-    "php": "~5.5.0|~5.6.0|~7.0.0|~7.1.0|~7.2.0",
+    "php": "~7.1.3|~7.2.0",
     "composer/composer": "~1.6.0",
     "symfony/console": "~4.0.0"
   },
   "require-dev": {
-    "phpunit/phpunit": "~6.2.0"
+    "phpunit/phpunit": "~7.0.0"
   },
   "autoload": {
     "psr-4": {