• Added support for STIX 2.1; 2.1 is now the default, but the --version option can be used to validate against the 2.0 specification instead (@clenk, @JohannKT, @ejratl, @emmanvg, @zrush-mitre, @chisholm)
• Added support for Python 3.8 (@rooterkyberian) and 3.9
• Dropped support for Python versions older than 3.5
• Updated --strict-types and --strict-properties to issue warnings instead of errors
• Fixed a bug with exiting when validator is used as a library
• Fixed a bug of failing silently if the local schema directory is empty (@zrush-mitre)