Bump autobahn from 19.5.1 to 20.12.3

Bumps [autobahn](https://github.com/crossbario/autobahn-python) from 19.5.1 to 20.12.3.
- [Release notes](https://github.com/crossbario/autobahn-python/releases)
- [Changelog](https://github.com/crossbario/autobahn-python/blob/master/docs/changelog.rst)
- [Commits](crossbario/autobahn-python@v19.5.1...v20.12.3)

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

requirements.txt

@@ -7,7 +7,7 @@ asn1crypto==0.24.0
 astroid==2.2.5
 async-timeout==2.0.1
 attrs==19.1.0
-autobahn==19.5.1
+autobahn==20.12.3
 Automat==0.7.0
 autopep8==1.4.4
 billiard==3.6.0.0