give the client a chance to run room.updatePendingEvent after sending

before the next event is sent. This is needed to update the target id
if it was the local id of the event that was just sent.

src/scheduler.js

@@ -220,7 +220,14 @@ function _processQueue(scheduler, queueName) {
     );
     // fire the process function and if it resolves, resolve the deferred. Else
     // invoke the retry algorithm.
-    scheduler._procFn(obj.event).done(function(res) {
+
+    // First wait for a resolved promise, so the resolve handlers for
+    // the deferred of the previously sent event can run.
+    // This way enqueued relations/redactions to enqueued events can receive
+    // the remove id of their target before being sent.
+    Promise.resolve().then(() => {
+        return scheduler._procFn(obj.event);
+    }).then(function(res) {
         // remove this from the queue
         _removeNextEvent(scheduler, queueName);
         debuglog("Queue '%s' sent event %s", queueName, obj.event.getId());