Update tox to 2.7.0

[pyup-bot]

There's a new version of tox available.
You are currently using 2.6.0. I have updated it to 2.7.0

These links might come in handy: PyPI | Changelog | Docs

Changelog

2.7.0

---

• p450: Stop after the first installdeps and first testenv create hooks
  succeed. This changes the default behaviour of tox_testenv_create
  and tox_testenv_install_deps to not execute other registered hooks when
  the first hook returns a result that is not None.
  Thanks Anthony Sottile (asottile).

• 271 and 464: Improve environment information for users.

New command line parameter: -a show all defined environments -
not just the ones defined in (or generated from) envlist.

New verbosity settings for -l and -a: show user defined descriptions
of the environments. This also works for generated environments from factors
by concatenating factor descriptions into a complete description.

Note that for backwards compatibility with scripts using the output of -l
it's output remains unchanged.

Thanks Gábor Bernát (gaborbernat).

• 464: Fix incorrect egg-info location for modified package_dir in setup.py.
  Thanks Selim Belhaouane (selimb).

• 431: Add 'LANGUAGE' to default passed environment variables.
  Thanks Paweł Adamczak (pawalad).

• 455: Add a Vagrantfile with a customized Arch Linux box for local testing.
  Thanks Oliver Bestwalter (obestwalter).

• 454: Revert 407, empty commands is not treated as an error.
  Thanks Anthony Sottile (asottile).

• 446: (infrastructure) Travis CI tests for tox now also run on OS X now.
  Thanks Jason R. Coombs (jaraco).

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖