Update yarl to 1.8.1

[pyup-bot]

This PR updates yarl from 1.7.2 to 1.8.1.

Changelog

1.8.1

==================

Misc
----

- `694 <https://github.com/aio-libs/yarl/issues/694>`_, `#699 <https://github.com/aio-libs/yarl/issues/699>`_, `#700 <https://github.com/aio-libs/yarl/issues/700>`_, `#701 <https://github.com/aio-libs/yarl/issues/701>`_, `#702 <https://github.com/aio-libs/yarl/issues/702>`_, `#703 <https://github.com/aio-libs/yarl/issues/703>`_, `#739 <https://github.com/aio-libs/yarl/issues/739>`_

1.8.0

==================

Features
--------

- Added ``URL.raw_suffix``, ``URL.suffix``, ``URL.raw_suffixes``, ``URL.suffixes``, ``URL.with_suffix``. (`613 <https://github.com/aio-libs/yarl/issues/613>`_)


Improved Documentation
----------------------

- Fixed broken internal references to :meth:`~URL.human_repr`. (`665 <https://github.com/aio-libs/yarl/issues/665>`_)
- Fixed broken external references to :doc:`multidict:index` docs. (`665 <https://github.com/aio-libs/yarl/issues/665>`_)


Deprecations and Removals
-------------------------

- Dropped Python 3.6 support. (`672 <https://github.com/aio-libs/yarl/issues/672>`_)


Misc
----

- `646 <https://github.com/aio-libs/yarl/issues/646>`_, `#699 <https://github.com/aio-libs/yarl/issues/699>`_, `#701 <https://github.com/aio-libs/yarl/issues/701>`_

Links

• PyPI: https://pypi.org/project/yarl
• Changelog: https://pyup.io/changelogs/yarl/
• Repo: https://github.com/aio-libs/yarl/