doc: Update URL for PL/PHP

Author: petere

doc/src/sgml/external-projects.sgml

@@ -178,7 +178,7 @@
      <row>
       <entry>PL/PHP</entry>
       <entry>PHP</entry>
-      <entry><ulink url="http://www.commandprompt.com/community/plphp/"></ulink></entry>
+      <entry><ulink url="https://public.commandprompt.com/projects/plphp"></ulink></entry>
      </row>
 
      <row>