Require phpstan/phpstan-phpunit

Author: westonruter

composer.json

@@ -21,7 +21,8 @@
     "szepeviktor/phpstan-wordpress": "^1.3.0",
     "wp-coding-standards/wpcs": "^2.2",
     "wp-phpunit/wp-phpunit": "^5.8",
-    "yoast/phpunit-polyfills": "^1.0"
+    "yoast/phpunit-polyfills": "^1.0",
+    "phpstan/phpstan-phpunit": "^1.3"
   },
   "require": {
     "composer/installers": "~1.0",