Update backports.functools_lru_cache to 1.6.1

[pyup-bot]

This PR updates backports.functools_lru_cache from 1.5.0 to 1.6.1.

Changelog

1.6.1

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Publish release notes on readthedocs.

1.6.0

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Refresh package metadata.
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Links

• PyPI: https://pypi.org/project/backports.functools-lru-cache
• Changelog: https://pyup.io/changelogs/backports.functools-lru-cache/
• Repo: https://github.com/jaraco/backports.functools_lru_cache

[systemcatch]

I'm not sure exactly why pyup is activated for this repo now? Regardless we need to be careful with this dependency upgrade due to #495

[jadchaar]

I think @andrewelkins added this recently. We definitely need to upgrade it though because all Arrow installs on 2.7 will most likely use 1.6.1 because we only require >=1.2.1 (https://github.com/crsmithdev/arrow/blob/master/setup.py#L28).

[andrewelkins]

Guilty. We're free to ignore any of the PRs that it sends, but at least we'll be aware they are available. If it's too noisy I can remove it or minimize the amount of PRs it sends.

[jadchaar]

Hah all good @andrewelkins. It is a great addition! We were just surprised by it :).