Remove illegal std::to_string definition and use ndn::to_string in its place

Change-Id: I81481fea3267bde669c45df182e0aea8ccd1a188
Refs: #3214
diff --git a/tools/ndn-autoconfig/base-dns.cpp b/tools/ndn-autoconfig/base-dns.cpp
index bcd1f65..c4f27b3 100644
--- a/tools/ndn-autoconfig/base-dns.cpp
+++ b/tools/ndn-autoconfig/base-dns.cpp
@@ -160,7 +160,7 @@
   std::string uri = "udp://";
   uri.append(hostName);
   uri.append(":");
-  uri.append(std::to_string(convertedPort));
+  uri.append(to_string(convertedPort));
 
   return uri;
 }