Update toc.xml

Update copyright date range.

Author: sarcanon

guidelines/xml/toc.xml

@@ -112,7 +112,7 @@ End license statement: do not remove -->
         <p>You can consult previous versions of the Guidelines in the <ref target="https://sourceforge.net/projects/epidoc/files/Guidelines/">Archive</ref> area of the Files section.</p>
         <p>To cite the EpiDoc Guidelines, please use the following information:</p>
         <quote>
-            <bibl>Tom Elliott, Gabriel Bodard, Elli Mylonas, Simona Stoyanova, Charlotte Tupman, Scott Vanderbilt, et al. (<date>2017-2025</date>), <title level="m">EpiDoc Guidelines: Ancient documents in TEI XML</title> (Version 9). Available: <ref target="https://epidoc.stoa.org/gl/latest/"
+            <bibl>Tom Elliott, Gabriel Bodard, Elli Mylonas, Simona Stoyanova, Charlotte Tupman, Scott Vanderbilt, et al. (<date>2017-2026</date>), <title level="m">EpiDoc Guidelines: Ancient documents in TEI XML</title> (Version 9). Available: <ref target="https://epidoc.stoa.org/gl/latest/"
                     >https://epidoc.stoa.org/gl/latest/</ref>.</bibl>
         </quote>
     </div>