With alpha2 without using the constraints https://github.com/apache/airflow/blob/constraints-master/constraints-3.6.txt , when accessing Webserver it fails with

```
Something bad has happened.
Please consider letting us know by creating a bug report using GitHub.

Python version: 3.6.12
Airflow version: 2.0.0a2
Node: 599861bd62ac
-------------------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 2447, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1953, in full_dispatch_request
    return self.finalize_request(rv)
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1970, in finalize_request
    response = self.process_response(response)
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 2269, in process_response
    self.session_interface.save_session(self, ctx.session, response)
  File "/usr/local/lib/python3.6/site-packages/flask/sessions.py", line 387, in save_session
    samesite=samesite,
  File "/usr/local/lib/python3.6/site-packages/werkzeug/wrappers/base_response.py", line 479, in set_cookie
    samesite=samesite,
  File "/usr/local/lib/python3.6/site-packages/werkzeug/http.py", line 1217, in dump_cookie
    raise ValueError("SameSite must be 'Strict', 'Lax', or 'None'.")
ValueError: SameSite must be 'Strict', 'Lax', or 'None'.
```
setup.py
'presto-python-client>=0.7.0,<0.8'
]
qds = [
    'qds-sdk>=1.10.4',
]
rabbitmq = [
    'amqp',
]
redis = [
    'redis~=3.2',
]
salesforce = [
    'simple-salesforce>=1.0.0',
]
samba = [
    'pysmbclient>=0.1.3',
]
segment = [
    'analytics-python>=1.2.9',
]
sendgrid = [
    'sendgrid>=6.0.0,<7',
]
sentry = [
    'blinker>=1.1',
    'sentry-sdk>=0.8.0',
]
singularity = ['spython>=0.0.56']
slack = [
    'slackclient>=2.0.0,<3.0.0',