Fixes link to structured typesetting version of the pages (#3611)

Author: tirix

set.mm

@@ -431553,7 +431553,7 @@ orthogonal vectors (i.e. whose inner product is 0) is the sum of the
 /* Optional link(s) to other versions of the theorem page.  A "*" is replaced
    with the label of the current theorem.  If you need a literal "*" as part
    of the URL, use the alternate URL encoding "%2A". */
-htmlexturl '<A HREF="http://metamath.tirix.org/*.html">'
+htmlexturl '<A HREF="http://metamath.tirix.org/mpests/*.html">'
     + 'Structured version</A>&nbsp;&nbsp; '
     + '<A HREF="https://expln.github.io/metamath/asrt/*.html">'
     + 'Visualization version</A>&nbsp;&nbsp; ';