[pushed] wwwdocs: readings: Update link to Polyhedron tests

Pushed.

polyhedron.com appears gone, now redirects to fortran.uk where I
found Polyhedron nested below.
---
 htdocs/readings.html | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/htdocs/readings.html b/htdocs/readings.html
index 4cbb38994..139a73ed8 100644
--- a/htdocs/readings.html
+++ b/htdocs/readings.html
@@ -443,7 +443,7 @@ names.
         Tests of run-time checking capabilities
         <ul>
           <li>
-            <a href="https://polyhedron.com">Polyhedron tests</a>
+            <a href="https://fortran.uk/fortran-compiler-comparisons/the-polyhedron-solutions-benchmark-suite/">Polyhedron tests</a>
           </li>
         </ul>
       </li>
-- 
2.55.0