Bump sanic from 0.8 to 20.12.6 in /examples/server/sanic (#875)

Bumps [sanic](https://github.com/sanic-org/sanic) from 0.8 to 20.12.6.
- [Release notes](https://github.com/sanic-org/sanic/releases)
- [Changelog](https://github.com/sanic-org/sanic/blob/main/CHANGELOG.rst)
- [Commits](sanic-org/sanic@0.8.0...v20.12.6)

---
updated-dependencies:
- dependency-name: sanic
  dependency-type: direct:production
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

examples/server/sanic/requirements.txt

@@ -2,7 +2,7 @@ aiofiles==0.3.0
 httptools==0.0.9
 python_engineio
 python_socketio
-sanic==0.8
+sanic==20.12.6
 six==1.10.0
 ujson==1.35
 uvloop==0.8.0