Fix missing underscore escape in 03-mpi-api

Author: aobolensk

03-mpi-api/03-mpi-api.tex

@@ -396,7 +396,7 @@ \section{Collective operations}
 \begin{frame}{References}
   \begin{enumerate}
     \item MPI Standard \href{https://www.mpi-forum.org/docs/}{https://www.mpi-forum.org/docs/}
-    \item Boost.MPI Chapter in Boost documentation \href{https://www.boost.org/doc/libs/1_86_0/doc/html/mpi.html}{https://www.boost.org/doc/libs/1_86_0/doc/html/mpi.html}
+    \item Boost.MPI Chapter in Boost documentation \href{https://www.boost.org/doc/libs/1_86_0/doc/html/mpi.html}{https://www.boost.org/doc/libs/1\_86\_0/doc/html/mpi.html}
     \item Open MPI v4.0.7 documentation: \href{https://www.open-mpi.org/doc/v4.0/}{https://www.open-mpi.org/doc/v4.0/}
   \end{enumerate}
 \end{frame}