Bump tornado from 6.0.3 to 6.0.4

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.0.3 to 6.0.4.
- [Release notes](https://github.com/tornadoweb/tornado/releases)
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.0.3...v6.0.4)

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

Author: dependabot-preview[bot]

requirements.txt

@@ -1,5 +1,5 @@
 tornado-cors==0.6.0
-tornado==6.0.3 # Because https://stackoverflow.com/questions/55452074/bokeh-serve-show-myapp
+tornado==6.0.4 # Because https://stackoverflow.com/questions/55452074/bokeh-serve-show-myapp
 lxml==4.4.2
 python-dotenv==0.12.0
 redis==3.3.11