make cryptography dep required

[wochinge]

Proposed changes:

• cryptography wasn't part of our Docker images which caused the validation of JWT tokens to fail
• upgrading PyJWT to it's latest version
• fixes this error when using Rasa X

2021-01-07T14:41:05.1125275Z �[36mrasa-x_1            |�[0m [2021-01-07 14:41:05 +0000] - (sanic.access)[INFO][172.18.0.12:55370]: GET http://rasa-x:5002/api/version  200 616
2021-01-07T14:41:05.2506098Z �[35;1mrasa-production_1   |�[0m 2021-01-07 14:41:05 ERROR    rasa.core.channels.rasa_chat  - Failed to decode bearer token.
2021-01-07T14:41:05.2509294Z �[35;1mrasa-production_1   |�[0m Traceback (most recent call last):
2021-01-07T14:41:05.2510788Z �[35;1mrasa-production_1   |�[0m   File "/opt/venv/lib/python3.7/site-packages/jwt/api_jws.py", line 219, in _verify_signature
2021-01-07T14:41:05.2512030Z �[35;1mrasa-production_1   |�[0m     alg_obj = self._algorithms[alg]
2021-01-07T14:41:05.2513002Z �[35;1mrasa-production_1   |�[0m KeyError: 'RS256'
2021-01-07T14:41:05.2513856Z �[35;1mrasa-production_1   |�[0m 
2021-01-07T14:41:05.2514948Z �[35;1mrasa-production_1   |�[0m During handling of the above exception, another exception occurred:
2021-01-07T14:41:05.2516000Z �[35;1mrasa-production_1   |�[0m 
2021-01-07T14:41:05.2517064Z �[35;1mrasa-production_1   |�[0m Traceback (most recent call last):
2021-01-07T14:41:05.2518399Z �[35;1mrasa-production_1   |�[0m   File "/opt/venv/lib/python3.7/site-packages/rasa/core/channels/rasa_chat.py", line 87, in _decode_bearer_token
2021-01-07T14:41:05.2527537Z �[35;1mrasa-production_1   |�[0m     return self._decode_jwt(bearer_token)
2021-01-07T14:41:05.2529501Z �[35;1mrasa-production_1   |�[0m   File "/opt/venv/lib/python3.7/site-packages/rasa/core/channels/rasa_chat.py", line 78, in _decode_jwt
2021-01-07T14:41:05.2530977Z �[35;1mrasa-production_1   |�[0m     authorization_header_value, self.jwt_key, algorithms=self.jwt_algorithm
2021-01-07T14:41:05.2532364Z �[35;1mrasa-production_1   |�[0m   File "/opt/venv/lib/python3.7/site-packages/jwt/api_jwt.py", line 92, in decode
2021-01-07T14:41:05.2534033Z �[35;1mrasa-production_1   |�[0m     jwt, key=key, algorithms=algorithms, options=options, **kwargs
2021-01-07T14:41:05.2535302Z �[35;1mrasa-production_1   |�[0m   File "/opt/venv/lib/python3.7/site-packages/jwt/api_jws.py", line 156, in decode
2021-01-07T14:41:05.2536294Z �[35;1mrasa-production_1   |�[0m     key, algorithms)
2021-01-07T14:41:05.2537604Z �[35;1mrasa-production_1   |�[0m   File "/opt/venv/lib/python3.7/site-packages/jwt/api_jws.py", line 226, in _verify_signature
2021-01-07T14:41:05.2538855Z �[35;1mrasa-production_1   |�[0m     raise InvalidAlgorithmError('Algorithm not supported')
2021-01-07T14:41:05.2540206Z �[35;1mrasa-production_1   |�[0m jwt.exceptions.InvalidAlgorithmError: Algorithm not supported

Status (please check what you already did):

• added some tests for the functionality
• updated the documentation
• updated the changelog (please check changelog for instructions)
• reformat files using black (please check Readme for instructions)