pluggy: Test builds at travis failing since release of pluggy v0.12

Hi all, Our test builds at StarKit began to unexpectedly fail since last 3 days. I checked this by doing some random changes in readme (https://travis-ci.org/jaladh-singhal/starkit/jobs/538727910) and they were still failing with same error:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/tmp/starkit-test-k6s1wpex/lib.linux-x86_64-3.6/starkit/_astropy_init.py", line 111, in test
    coverage=coverage, open_files=open_files, **kwargs)
  File "/home/travis/miniconda2/envs/starkit/lib/python3.6/site-packages/astropy/tests/runner.py", line 518, in run_tests
    return super(TestRunner, self).run_tests(**kwargs)
  File "/home/travis/miniconda2/envs/starkit/lib/python3.6/site-packages/astropy/tests/runner.py", line 206, in run_tests
    return pytest.main(args=args, plugins=self.keywords['plugins'])
  File "_pytest.config", line 38, in main
  File "_pytest.config", line 117, in _prepareconfig
  File "_pytest.vendored_packages.pluggy", line 724, in __call__
  File "_pytest.vendored_packages.pluggy", line 338, in _hookexec
  File "_pytest.vendored_packages.pluggy", line 333, in <lambda>
  File "_pytest.vendored_packages.pluggy", line 595, in execute
  File "_pytest.vendored_packages.pluggy", line 249, in _wrapped_call
  File "_pytest.helpconfig", line 28, in pytest_cmdline_parse
  File "_pytest.vendored_packages.pluggy", line 278, in get_result
  File "_pytest.vendored_packages.pluggy", line 264, in __init__
  File "_pytest.vendored_packages.pluggy", line 596, in execute
  File "_pytest.config", line 852, in pytest_cmdline_parse
  File "_pytest.config", line 957, in parse
  File "_pytest.config", line 918, in _preparse
  File "_pytest.vendored_packages.pluggy", line 501, in load_setuptools_entrypoints
  File "/home/travis/miniconda2/envs/starkit/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2433, in load
    self.require(*args, **kwargs)
  File "/home/travis/miniconda2/envs/starkit/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2456, in require
    items = working_set.resolve(reqs, env, installer, extras=self.extras)
  File "/home/travis/miniconda2/envs/starkit/lib/python3.6/site-packages/pkg_resources/__init__.py", line 791, in resolve
    raise VersionConflict(dist, req).with_context(dependent_req)
pkg_resources.ContextualVersionConflict: (importlib-metadata 0.0.0 (/home/travis/miniconda2/envs/starkit/lib/python3.6/site-packages), Requirement.parse('importlib-metadata>=0.12'), {'pluggy'})
The command "python setup.py $SETUP_CMD" exited with 1.

I further investigated and found that pluggy has been recently updated to v0.12.0 (on May 28) and since then only our travis builds are failing that are using SETUP_CMD='test --coverage'. FYI, it is an Astropy testing framework that runs pytest by passing option coverage to generate a coverage report. As much as I could understand, I noticed that pluggy is never used by us directly, it is somehow used by pytest under the hood (I may be wrong)?! Thus I resorted here to inform you about the issue to help us solve the problem. Is it somehow related to issue https://github.com/pytest-dev/pluggy/issues/205?

Thanks in advance. Please let’s try to fix this soon 😃