send update.document out (#56)

while it is not displayed currented in the emulator
(which would be nice, same as summary and info),
a webxdc may still use the received update.document value.

therefore, it is important to send out out.

Author: r10s

webxdc.js

@@ -55,6 +55,7 @@ window.webxdc = (() => {
         payload: update.payload,
         summary: update.summary,
         info: update.info,
+        document: update.document,
         serial: serial,
       };
       updates.push(_update);