Run bin/buildout got warning

While I build the project by ./bin/buildout, it will show the error as below.

> Error: The extension buildout-versions is now included in buildout itself.
> Remove the extension from your configuration and look at the `show-picked-versions`
> option in buildout's documentation.

I update the buildout.cfg as my commit.

Thanks!

FYI: https://pypi.python.org/pypi/zc.buildout/2.0.0