message: Fix comments in unread room tracking
  A few comments mention read marker where they really mean read receipt.
diff: @@ -70,20 +70,20 @@ module.exports = {
  const ev = room.timeline[i];
  if (ev.getId() == readUpToId) {
  - // If we've read up to this event, there's nothing more recents
  + // If we've read up to this event, there's nothing more recent
  // that counts and we can stop looking because the user's read
  // this and everything before.
  return false;
  } else if (!shouldHideEvent(ev) && this.eventTriggersUnreadCount(ev)) {
  // We've found a message that counts before we hit
  - // the read marker, so this room is definitely unread.
  + // the user's read receipt, so this room is definitely unread.
  return true;
  }
  }
  - // If we got here, we didn't find a message that counted but didn't
  - // find the read marker either, so we guess and say that the room
  - // is unread on the theory that false positives are better than
  - // false negatives here.
  + // If we got here, we didn't find a message that counted but didn't find
  + // the user's read receipt either, so we guess and say that the room is
  + // unread on the theory that false positives are better than false
  + // negatives here.
  return true;
  },
  };
  