py3: return unicode from setup.py's get_version

py3 expects the version number for eggs to be unicode, so despite 9.2.0 being
the first evolve release with beta py3 support it isn't currently pip
installable since it dies with:

    File "*/setuptools/command/egg_info.py", line *, in tagged_version
      return safe_version(version + self.vtags)
  TypeError: can't concat str to bytes

The `setup.py install` test added in a previous commit should cover this since
it died in a different but similar way before.

--HG--
branch : stable
2 jobs for topic/stable/py3install in 12 minutes and 13 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Test
passed flake8 #29128

00:00:16

passed tests #29129

00:12:13