[e-acsl:refman] add a word about loop variants in the changes

src/plugins/e-acsl/doc/refman/changes_modern.tex

@@ -179,6 +179,7 @@ in \lstinline|\\at|}
 \item \changeinsection{expressions}{mark logic function and predicate
   applications as implemented}
 \item \changeinsection{fn-behavior}{mark admit and check clauses as implemented}
+\item \changeinsection{loop_annot}{mark loop variants as implemented}
 \end{itemize}
 
 \subsection*{Version Titanium-22}