tests: stop using deprecated Buffer::buf()

Change-Id: I48b7672098cfe57ccb470a247eed0c80e24cfffe
diff --git a/tests/daemon/face/stream-transport.t.cpp b/tests/daemon/face/stream-transport.t.cpp
index ad8d60c..81044d1 100644
--- a/tests/daemon/face/stream-transport.t.cpp
+++ b/tests/daemon/face/stream-transport.t.cpp
@@ -1,5 +1,5 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
+/*
  * Copyright (c) 2014-2017,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
@@ -111,8 +111,8 @@
   Block pkt1 = ndn::encoding::makeStringBlock(300, "hello");
   Block pkt2 = ndn::encoding::makeStringBlock(301, "world");
   ndn::Buffer buf(pkt1.size() + pkt2.size());
-  std::copy(pkt1.begin(), pkt1.end(), buf.buf());
-  std::copy(pkt2.begin(), pkt2.end(), buf.buf() + pkt1.size());
+  std::copy(pkt1.begin(), pkt1.end(), buf.begin());
+  std::copy(pkt2.begin(), pkt2.end(), buf.begin() + pkt1.size());
 
   this->remoteWrite(buf);