[wwwdocs] Update re C++ moved to gnu++14

[Marek Polacek]

Applied.

Index: changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-6/changes.html,v
retrieving revision 1.18
diff -u -r1.18 changes.html
--- changes.html        27 Jul 2015 14:36:20 -0000      1.18
+++ changes.html        31 Jul 2015 12:05:52 -0000
@@ -13,7 +13,10 @@
 
 <!-- .................................................................. -->
 <h2>Caveats</h2>
-
+  <ul>
+    <li>The default mode for C++ is now <code>-std=gnu++14</code> instead of
+        <code>-std=gnu++98</code>.</li>
+  </ul>
 
 <!-- .................................................................. -->
 <h2 id="general">General Optimizer Improvements</h2>
@@ -63,6 +66,9 @@
   </ul>
 
 <h3 id="cxx">C++</h3>
+  <ul>
+    <li>The default mode has been changed to <code>-std=gnu++14</code>.</li>
+  </ul>
 
 <h3 id="fortran">Fortran</h3>
   <ul>

        Marek