Bump multidict from 4.7.6 to 5.0.0

Bumps [multidict](https://github.com/aio-libs/multidict) from 4.7.6 to 5.0.0.
- [Release notes](https://github.com/aio-libs/multidict/releases)
- [Changelog](https://github.com/aio-libs/multidict/blob/master/CHANGES.rst)
- [Commits](aio-libs/multidict@v4.7.6...v5.0.0)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -13,7 +13,7 @@ cffi==1.14.3              # via pycares
 chardet==3.0.4            # via aiohttp
 fonttools==4.16.1         # via fdiff (setup.py)
 idna==2.10                # via yarl
-multidict==4.7.6          # via aiohttp, yarl
+multidict==5.0.0          # via aiohttp, yarl
 pycares==3.1.1            # via aiodns
 pycparser==2.20           # via cffi
 yarl==1.6.0               # via aiohttp