Added 'Require all granted' to httpd.conf example

When following the original httpd.conf example, `http://localhost/phpmyadmin/` had a 403 error. I followed @james2doyle's recommendation in [issue 1234](https://github.com/Homebrew/homebrew-php/issues/1234) and the error stopped.

If there is a better fix for this, kindly advise.