[wwwdocs] Mention libstdc++-v3 <regex> in 4.9 changes.html

[Jonathan Wakely]

On 2 October 2013 15:52, Tim Shen wrote:
> I feel little bit uncomfortable with "new ISO C++ standard, C++11",
> since C++14 is already there, so I removed it.

Good idea.

> Please check the words, since English is not my first language >.<

The english is fine, please wait a few hours in case anyone else has
comments, but if you don't hear anything else you can go ahead and
commit it.