MITRE TAXII server doesn't support 2.1, but 2.0.

[Cyb3rWard0g]

Yesterday a new version of taxii2-client (oasis-open / cti-taxii-client) was released (version 2.0.0) and this results in an error in attackcti:

Traceback (most recent call last):
File "/Users/ruben/vscode-projects/vscode-attackcti/testit.py", line 4, in
mitre = attack_client()
File "/Users/ruben/vscode-projects/venv-attackcti/lib/python3.8/site-packages/attackcti-0.3.1-py3.8.egg/attackcti/attack_api.py", line 46, in init
File "/Users/ruben/vscode-projects/venv-attackcti/lib/python3.8/site-packages/stix2-1.3.1-py3.8.egg/stix2/datastore/taxii.py", line 164, in init
raise DataSourceError(
stix2.datastore.DataSourceError: The underlying TAXII Collection resource defined in the supplied
Ruben Bouman:
TAXII Collection object provided could not be reached. Recieved error: "406 Client Error: Not Acceptable for url: https://cti-taxii.mitre.org/stix/collections/95ecc380-afe9-11e4-9b6c-751b66dd541e/"

I've investigated the issue and it's because taxii2-client now load TAXII 2.1 classes by default. And the MITRE TAXII server doesn't support 2.1, but 2.0.
When having taxtii2client already installed, there's no problem. But when you install attackcti in a fresh clean environment, taxii2-client==2.0.0 will be installed as dependency.
In my opinion there are two solutions:

• Import the 2.0 Collection class in attack_api.py: from taxii2client.v20 import Collection (line 14). This is also mentioned in the release page of taxii2-client: https://github.com/oasis-open/cti-taxii-client/releases
• Somehow make sure when attackcti is installed on a system, that taxii2-client==1.0.1 is installed instead of 2.0.0. I'm not sure how this works and if it's possible.
  I've tested the first bullet and that's working. Please let me know how what your opinion is and how we can try to tackle this the best way.