[wwwdocs] gcc-6/changes.html - fix reference to C++17

[Gerald Pfeifer]

While working on a proper redirect for projects/cxx1z.html, I 
noticed that the link below doesn't really work as desired, since 
the anchor actually is cxx1z without the .html.

Question: should we change this to cxx17 now?

Applied for now.

Gerald

Index: gcc-6/changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-6/changes.html,v
retrieving revision 1.96
diff -u -r1.96 changes.html
--- gcc-6/changes.html	27 Feb 2017 22:33:44 -0000	1.96
+++ gcc-6/changes.html	11 Mar 2017 15:55:41 -0000
@@ -296,7 +296,7 @@
     a memory store to a location precedes a constructor to that
     memory location.</li>
     <li>G++ now supports
-        <a href="https://gcc.gnu.org/projects/cxx-status.html#cxx1z.html">C++17</a>
+        <a href="https://gcc.gnu.org/projects/cxx-status.html#cxx1z">C++17</a>
         fold expressions, <code>u8</code> character literals,
         extended <code>static_assert</code>, and nested namespace definitions.</li>
     <li>G++ now allows constant evaluation for all non-type template arguments.</li>