Added doi to AgentPump1Pipe.mo (#4085)

This adds the DOI. The old link is no longer valid.

Buildings/DHC/Networks/Controls/AgentPump1Pipe.mo

@@ -228,8 +228,11 @@ the nominal value of the agent heat exchanger pinch point temperature difference
 </p>
 <h4>References</h4>
 <p>
-Ettore Zanetti, David Blum, Michael Wetter <a href=\"https://www.conftool.com/modelica2023/index.php?page=browseSessions\">
-Control development and sizing analysis for a 5th generation district heating and cooling network using Modelica</a>, 2023 International Modelica conference proceedings.
+Ettore Zanetti, David Blum, Michael Wetter.<br/>
+<a href=\"https://doi.org/10.3384/ecp20423\">
+Control development and sizing analysis for a 5th generation district heating and cooling network using Modelica</a>.<br/>
+Proc. of the 15th International Modelica Conference,
+p. 23--32, Aachen, Germany, October 2023.
 </p>
 </html>"));
 end AgentPump1Pipe;