Update stix objects, not regenerate

[yugoslavskiy]

For now, on a PoC stage, we regenerate STIX file on each execution. The main reason for that, is because it was developed to make ATT&CK Navigator work for RE&CT analytics.

So, it's impossible for other projects to use our STIX file in its current state. We need to update STIX objects, not rebuild them.

The current version of the script that is used for STIX generation could be found here.