Bump autobahn from 20.7.1 to 20.12.3

Bumps [autobahn](https://github.com/crossbario/autobahn-python) from 20.7.1 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](https://github.com/crossbario/autobahn-python/compare/v20.7.1...v20.12.3)

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

requirements.txt

@@ -2,7 +2,7 @@ aioredis==1.3.1
 asgiref==3.2.10
 async-timeout==3.0.1
 attrs==19.3.0
-autobahn==20.7.1
+autobahn==20.12.3
 Automat==20.2.0
 certifi==2020.6.20
 cffi==1.14.2