Incompatible absl-py version with tensorflow-metadata

[Suikaba]

In the latest blueoil, the following error occurs when blueoil train:

Traceback (most recent call last):
File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 567, in _build_master
    ws.require(__requires__)
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 884, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 775, in resolve
    raise VersionConflict(dist, req).with_context(dependent_req)
pkg_resources.ContextualVersionConflict: (absl-py 0.8.1 (/usr/local/lib/python3.6/dist-packages), Requirement.parse('absl-py<0.11,>=0.9'), {'tensorflow-metadata'})

In setup.cfg, force to use absl-py 0.8.1 (#1168). I think it is better to use absl-py 0.9 or higher version.