Fix typo in yardoc for #download_request_body

Author: rastating

lib/wpxf/wordpress/file_download.rb

@@ -50,7 +50,7 @@ def download_request_params
     nil
   end
 
-  # @return [Hash, String] the body to be use when requesting the download file.
+  # @return [Hash, String] the body to be used when requesting the download file.
   def download_request_body
     nil
   end