Bump yarl from 1.5.1 to 1.6.3

Bumps [yarl](https://github.com/aio-libs/yarl) from 1.5.1 to 1.6.3.
- [Release notes](https://github.com/aio-libs/yarl/releases)
- [Changelog](https://github.com/aio-libs/yarl/blob/master/CHANGES.rst)
- [Commits](aio-libs/yarl@v1.5.1...v1.6.3)

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

requirements.txt

@@ -14,4 +14,4 @@ pycparser==2.20
 six==1.15.0
 typing-extensions==3.7.4.3
 uvloop==0.14.0
-yarl==1.5.1
+yarl==1.6.3