Fix compilation against the latest ndn-cxx library

Change-Id: Ib9ae9c1601359a81a7f131ab63803f11adba7f38
diff --git a/core/logger-response.cpp b/core/logger-response.cpp
index bb796ad..c36f932 100644
--- a/core/logger-response.cpp
+++ b/core/logger-response.cpp
@@ -54,9 +54,9 @@
                                                m_msg.size());
   }
   else {
-    totalLength += ndn::prependNonNegativeIntegerBlock(block, tlv::DataSeqNo, m_dataSeqNo);
+    totalLength += prependNonNegativeIntegerBlock(block, tlv::DataSeqNo, m_dataSeqNo);
   }
-  totalLength += ndn::prependNonNegativeIntegerBlock(block, tlv::ResultCode, m_code);
+  totalLength += prependNonNegativeIntegerBlock(block, tlv::ResultCode, m_code);
 
   totalLength += block.prependVarNumber(totalLength);
   totalLength += block.prependVarNumber(tlv::LogResponse);