Bump graphene from 2.1.9 to 3.4.3 in /demos

Bumps [graphene](https://github.com/graphql-python/graphene) from 2.1.9 to 3.4.3.
- [Release notes](https://github.com/graphql-python/graphene/releases)
- [Commits](graphql-python/graphene@v2.1.9...v3.4.3)

---
updated-dependencies:
- dependency-name: graphene
  dependency-version: 3.4.3
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

demos/graphql-demo/requirements-dev.txt

@@ -4,7 +4,7 @@ aiohttp-graphql==1.1.0
 aiodataloader==0.4.2
 faker==37.8.0
 trafaret_config==2.0.2
-graphene==2.1.9
+graphene==3.4.3
 graphql-core==2.3.2
 graphql-ws==0.4.4
 psycopg2-binary==2.9.10