Fix setup.py

[MinchinWeb]

Tried to install the project (pip install -e .) and it broke with the following error:

'install_requires' must be a string or list of strings containing valid project/version requirement specifiers; Unordered types are not allowed

This pull request is a one-line change to return the requirements as a tuple rather than a set, and thus allow the project to install.

I'm on Python 3.6.3 on Windows 10 x64.

[SpotlightKid]

Uh, when did pip change in this manner?

[jmaupetit]

I encountered the same behavior recently.

[jmaupetit]

Looks good to me. Thanks!

[jmaupetit]

Looks like we also have to fix (or ignore) this new E722 flake8 rule.

[MinchinWeb]

I could fix the flake8 error simply enough.

The remaining Travis-CI failure is Python 3.3, because pytest dropped support with version 3.3.0, released about 2 weeks ago. Should support for Python 3.3 be dropped here too? Alternately, pytest could be pinned to v3.2.5, but I don't know enough about tox to pull that off myself.

[SpotlightKid]

Alternately, pytest could be pinned to v3.2.5, but I don't know enough about tox to pull that off myself.

Changing line 7 in tox.ini to:

    pytest<=3.2.5

should do the trick.

Unfortunately there's also a problem with arrow and Python 2.7. Arrpow release 0.11.0 and 0.12.0 have broken dependencies for Python 2.7 (backports.functools_lru_cache is not declared). So we have to also put

arrow<0.11.0

in requirements.txt for all tests to pass when running tox (without any existing virtualenv).

[MinchinWeb]

@SpotlightKid see #180 for an alternate way of dealing with the requirement issue.

[ghost]

This is preventing me from installing the AUR version, it just fails with 'install_requires' must be a string or list of strings containing valid project/version requirement specifiers; Unordered types are not allowed.

Mind publishing a new release if this fixed it?