Merge pull request #7 from php-api-clients/dependabot/composer/phpunit/phpunit-6.0.8

[Security] Bump phpunit/phpunit from 5.5.4 to 6.0.8

Author: WyriHaximus

composer.json

@@ -11,7 +11,7 @@
     "php": "^7.0"
   },
   "require-dev": {
-    "phpunit/phpunit": "^5.2.3",
+    "phpunit/phpunit": "^6.0.8",
     "squizlabs/php_codesniffer": "^3.4",
     "phake/phake": "^2.3"
   },