Bump aiohttp from 2.3.9 to 3.1.2

[dependabot-preview]

Bumps aiohttp from 2.3.9 to 3.1.2.

Changelog

Sourced from aiohttp's changelog.

3.0.9 (2018-03-14)

• Close a connection if an unexpected exception occurs while sending a request
  (#2827)

3.0.8 (2018-03-12)

• Use asyncio.current_task() on Python 3.7 (#2825)

3.0.7 (2018-03-08)

• Fix SSL proxy support by client. (#2810)
• Restore a imperative check in setup.py for python version. The check
  works in parallel to environment marker. As effect a error about unsupported
  Python versions is raised even on outdated systems with very old
  setuptools version installed. (#2813)

3.0.6 (2018-03-05)

• Add _reuse_address and _reuse_port to
  web_runner.TCPSite.__slots__. (#2792)

3.0.5 (2018-02-27)

• Fix InvalidStateError on processing a sequence of two
  RequestHandler.data_received calls on web server. (#2773)

3.0.4 (2018-02-26)

• Fix IndexError in HTTP request handling by server. (#2752)
• Fix MultipartWriter.append* no longer returning part/payload. (#2759)

3.0.3 (2018-02-25)

• Relax attrs dependency to minimal actually supported version
  17.0.3 The change allows to avoid version conflicts with currently
  existing test tools.

3.0.2 (2018-02-23)

... (truncated)

Commits

• ae2dbcb Bump to 3.1.2
• 2ba20de Add missing changenote
• 33daec0 [3.1] Make LineTooLong exception more detailed about actual data size (GH-286...
• db7dcb8 Backport 6a6ab7d and c5d399 to 3.1 (#2915)
• 98c7491 Don't install cherry_picker on Python 3.5
• d7f0511 Setup cherry_picker tool
• b02206a Bump to aiohttp 3.1.1
• 94295e5 Update CHANGES
• 9f2de0d Async iterators payload (#2873)
• 77623f8 Add an introcuctory to aiohttp 3.1 release
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #39.