Fix URL

Author: haukex

web/regex_tester.html

@@ -489,7 +489,7 @@
 
 <div style="margin-top:1em;font-size:0.8em">
 Author, Copyright, and License: see
-<a href="https://github.com/haukex/webperl/blob/master/web/regex_demo.html" target="_blank">the source code of this file</a>.<br/>
+<a href="https://github.com/haukex/webperl/blob/master/web/regex_tester.html" target="_blank">the source code of this file</a>.<br/>
 </div>
 
 </body>