chore(identify): Update phpunit/phpunit dependency to ~6.0

Author: unicodeveloper

composer.json

@@ -16,7 +16,7 @@
     "sinergi/browser-detector": "6.1.*"
    },
    "require-dev": {
-    "phpunit/phpunit": "5.3.*",
+    "phpunit/phpunit": "~6.0.0",
     "mockery/mockery": "0.9.*",
     "scrutinizer/ocular": "~1.1",
     "satooshi/php-coveralls": "^0.7.0"