Update multidict to 4.7.6

[pyup-bot]

This PR updates multidict from 4.7.4 to 4.7.6.

Changelog

4.7.6

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

Bugfixes
--------

- Fixed an issue with some versions of the ``wheel`` dist
failing because of being unable to detect the license file.
`481 <https://github.com/aio-libs/multidict/issues/481>`_


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4.7.5

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

Bugfixes
--------

- Fixed creating and updating of MultiDict from a sequence of pairs and keyword arguments. Previously passing a list argument modified it inplace, and other sequences caused an error.
`457 <https://github.com/aio-libs/multidict/issues/457>`_
- Fixed comparing with mapping: an exception raised in the
:py:func:`~object.__len__` method caused raising a SyntaxError.
`459 <https://github.com/aio-libs/multidict/issues/459>`_
- Fixed comparing with mapping: all exceptions raised in the
:py:func:`~object.__getitem__` method were silenced.
`460 <https://github.com/aio-libs/multidict/issues/460>`_


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Links

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