Make options optional again

This was done incorrectly in #65

Author: ruudk

Diff for: src/MultipartStreamBuilder.php

@@ -93,8 +93,8 @@ public function addData($resource, array $headers = [])
      *
      * @param string                                                      $name     the formpost name
      * @param string|resource|StreamInterface                             $resource
-     * @param array{'headers': array<string, string>, 'filename': string} $options
-     *
+     * @param array{'headers?': array<string, string>, 'filename?': string} $options
+     
      * Options:
      * - headers: additional headers as hashmap ['header-name' => 'header-value']
      * - filename: used to determine the mime type