labs/tools/heritage depends on pywikibot which is currently 2.0rc1.post2 in Pypi:
...
File ".tox/py27/lib/python2.7/site-packages/pywikibot/site.py", line 2147, in _build_namespaces
is_mw114 = MediaWikiVersion(self.version()) >= MediaWikiVersion('1.14')
File "python2.7/distutils/version.py", line 40, in __init__
self.parse(vstring)
File ".tox/py27/lib/python2.7/site-packages/pywikibot/tools/__init__.py", line 331, in parse
raise ValueError('Invalid version number "{0}"'.format(vstring))
ValueError: Invalid version number "1.27.0-wmf.1":-(