MAGETWO-71061: Remove zend json from migration #10341

 - fixed docBlock

Author: Oleksii Korshenko

lib/internal/Magento/Framework/Module/Setup/Migration.php

@@ -704,7 +704,7 @@ public function getCompositeModules()
      *
      * @param string $encodedValue
      * @param int $objectDecodeType
-     * @return array|bool|float|int|mixed|null|string
+     * @return string|int|float|bool|array|null
      * @throws \InvalidArgumentException
      * @SuppressWarnings(PHPMD.UnusedFormalParameter)
      * @deprecated
@@ -720,7 +720,7 @@ protected function _jsonDecode($encodedValue, $objectDecodeType = 1)
      * encoded in the JSON format
      *
      * @param string $encodedValue
-     * @return array|bool|float|int|mixed|null|string
+     * @return string|int|float|bool|array|null
      * @throws \InvalidArgumentException
      */
     private function jsonDecode($encodedValue)