Add six to install_requires

[koobs]

six is a documented dependency, add it to install_requires accordingly

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[soupytwist]

Thanks for adding this! If you accept the CLA (https://cla.developers.google.com/) I can merge.

[koobs]

@soupytwist Hi Nick! I'm not too keen to sign a CLA at the moment, especially for such a small, metadata only change, but happy for you to close this, replace it with a PR of your own, or create an issue instead. If there are better alternatives, I'm all ears

[soupytwist]

I've added this in the latest commit. Thanks for your help!

[koobs]

@soupytwist Thank you Nick, my pleasure :)