added missing global

extension/core/bg/download.js

@@ -18,7 +18,7 @@
  *   along with SingleFile.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-/* global browser, singlefile, Blob */
+/* global browser, singlefile, Blob, URL */
 
 singlefile.download = (() => {