transport: fix compilation with clang 7

Change-Id: I167fee0e8505c9a55b6617513045e1841a4ae70a
diff --git a/ndn-cxx/transport/detail/stream-transport-impl.hpp b/ndn-cxx/transport/detail/stream-transport-impl.hpp
index 8df5edd..6210b38 100644
--- a/ndn-cxx/transport/detail/stream-transport-impl.hpp
+++ b/ndn-cxx/transport/detail/stream-transport-impl.hpp
@@ -198,7 +198,7 @@
         }
 
         m_rxBufferSize += nBytesRecvd;
-        auto unparsedBytes = span(m_rxBuffer).first(m_rxBufferSize);
+        auto unparsedBytes = make_span(m_rxBuffer).first(m_rxBufferSize);
         while (!unparsedBytes.empty()) {
           auto [isOk, element] = Block::fromBuffer(unparsedBytes);
           if (!isOk) {