Update reference to amsmath documentation in example documents

example/mu/example.dtx

@@ -966,7 +966,7 @@ f \\
 \end{enumerate}
 For the complete list of environments and commands, consult the
 \textsf{amsmath} package manual\footnote{
-  See \url{http://mirrors.ctan.org/macros/latex/required/amslatex/math/amsldoc.pdf}.
+  See \url{http://mirrors.ctan.org/macros/latex/required/amsmath/amsldoc.pdf}.
   The \texttt{\textbackslash url} command is provided by the
   package \textsf{url}.
 }.