xmlstarlet not installed under new python version

[perestoronin]

error in xmlstarlet setup command: 'python_requires' must be
           a string containing valid version specifiers; Invalid specifier: '>=3.6.*'
      [end of output]

PR to possible solution

[dimitern]

Thanks! I've started the pipeline, but I suspect more changes will be needed to get it to work on newer versions of Python. My original idea was to support as far back as it makes sense, hence due to having to support 3.6 I had to avoid upgrading a bunch of dependencies. I'll spend some time on this soon and get it to work hopefully