Flower - Tornado version in dependency preventing start

[rich5851]

What happened before?

Flower started with no issues

What happens now?

celeryworker_1 | File "/usr/local/lib/python3.6/site-packages/flower/api/tasks.py", line 83, in TaskApply
celeryworker_1 | @web.asynchronous
celeryworker_1 | AttributeError: module 'tornado.web' has no attribute 'asynchronous'

Last stable commit / Since when?

Steps to reproduce

docker local and production setup with celery and flower
docker-compose build and docker-compose run

Fixed by adding tornado==4.5.2 at the bottom of requirements/base.txt

[luzfcb]

Thanks to report, but is duplicated to #1949