Requirement and formatting fixes (#5)

Add ext-json to composer requirements
Update editorconfig to match core
Update phpdoc to not reference missing import

php-packages/testing/src/integration/Extension/ExtensionManagerIncludeCurrent.php

@@ -16,7 +16,7 @@ use Illuminate\Support\Arr;
 class ExtensionManagerIncludeCurrent extends ExtensionManager
 {
     /**
-     * @return Collection
+     * @{@inheritDoc}
      */
     public function getExtensions()
     {