Bump multidict from 4.7.6 to 5.0.0 (#381)

Author: dependabot-preview[bot]

requirements-dev.txt

@@ -8,7 +8,7 @@ jinja2==2.11.2
 pytest==6.1.1
 pytest-cov==2.10.1
 yarl==1.6.0
-multidict==4.7.6
+multidict==5.0.0
 pytest-aiohttp==0.3.0
 pytest-sugar==0.9.4
 mypy==0.790