don't double-encode JSON

src/xhrListener.ts

@@ -79,10 +79,10 @@ class XhrListener {
         for (let client of c.clients) {
           let nonce: string = crypto.randomBytes(4).toString("hex");
           // TODO: verify the nonce against the received reply, which we currently ignore
-          client.directMessage(JSON.stringify({
+          client.directMessage({
             message_type: "broadcast",
             message: { event_type: event, seq_id: nonce, examId: archMsg.examId }
-          }));
+          });
           dmCount++;
         }
         // dmCount of 1 would be normal. more than 1 is odd, but not necessarily bad. 0 means Exam UI has gone away somehow.