Added missing self return type to ConfigInterface::registerCustomFixers()

src/ConfigInterface.php

@@ -108,6 +108,8 @@ interface ConfigInterface
      * Name of custom fixer should follow `VendorName/rule_name` convention.
      *
      * @param FixerInterface[]|iterable|\Traversable $fixers
+     *
+     * @return self
      */
     public function registerCustomFixers($fixers);