Update attrs to 18.1.0

[pyup-bot]

This PR updates attrs from 17.4.0 to 18.1.0.

Changelog

18.1.0

-------------------

Changes
^^^^^^^

- ``x=X(); x.cycle = x; repr(x)`` will no longer raise a ``RecursionError``, and will instead show as ``X(x=...)``.

`95 <https://github.com/python-attrs/attrs/issues/95>`_
- ``attr.ib(factory=f)`` is now syntactic sugar for the common case of ``attr.ib(default=attr.Factory(f))``.

`178 <https://github.com/python-attrs/attrs/issues/178>`_,
`356 <https://github.com/python-attrs/attrs/issues/356>`_
- Added ``attr.field_dict()`` to return an ordered dictionary of ``attrs`` attributes for a class, whose keys are the attribute names.

`290 <https://github.com/python-attrs/attrs/issues/290>`_,
`349 <https://github.com/python-attrs/attrs/issues/349>`_
- The order of attributes that are passed into ``attr.make_class()`` or the ``these`` argument of ``attr.s()`` is now retained if the dictionary is ordered (i.e. ``dict`` on Python 3.6 and later, ``collections.OrderedDict`` otherwise).

Before, the order was always determined by the order in which the attributes have been defined which may not be desirable when creating classes programatically.

`300 <https://github.com/python-attrs/attrs/issues/300>`_,
`339 <https://github.com/python-attrs/attrs/issues/339>`_,
`343 <https://github.com/python-attrs/attrs/issues/343>`_
- In slotted classes, ``__getstate__`` and ``__setstate__`` now ignore the ``__weakref__`` attribute.

`311 <https://github.com/python-attrs/attrs/issues/311>`_,
`326 <https://github.com/python-attrs/attrs/issues/326>`_
- Setting the cell type is now completely best effort.
This fixes ``attrs`` on Jython.

We cannot make any guarantees regarding Jython though, because our test suite cannot run due to dependency incompatabilities.

`321 <https://github.com/python-attrs/attrs/issues/321>`_,
`334 <https://github.com/python-attrs/attrs/issues/334>`_
- If ``attr.s`` is passed a *these* argument, it will not attempt to remove attributes with the same name from the class body anymore.

`322 <https://github.com/python-attrs/attrs/issues/322>`_,
`323 <https://github.com/python-attrs/attrs/issues/323>`_
- The hash of ``attr.NOTHING`` is now vegan and faster on 32bit Python builds.

`331 <https://github.com/python-attrs/attrs/issues/331>`_,
`332 <https://github.com/python-attrs/attrs/issues/332>`_
- The overhead of instantiating frozen dict classes is virtually eliminated.
`336 <https://github.com/python-attrs/attrs/issues/336>`_
- Generated ``__init__`` methods now have an ``__annotations__`` attribute derived from the types of the fields.

`363 <https://github.com/python-attrs/attrs/issues/363>`_
- We have restructured the documentation a bit to account for ``attrs``' growth in scope.
Instead of putting everything into the `examples <http://www.attrs.org/en/stable/examples.html>`_ page, we have started to extract narrative chapters.

So far, we've added chapters on `initialization <http://www.attrs.org/en/stable/init.html>`_ and `hashing <http://www.attrs.org/en/stable/hashing.html>`_.

Expect more to come!

`369 <https://github.com/python-attrs/attrs/issues/369>`_,
`370 <https://github.com/python-attrs/attrs/issues/370>`_


----

Links

• PyPI: https://pypi.org/project/attrs
• Changelog: https://pyup.io/changelogs/attrs/
• Homepage: http://www.attrs.org/

Resolves #111