Update pip-shims vendor to 0.3.0.

[n6g7]

The issue

Fixes #2924 by updating the pip-shims vendor to v0.3.0.

The fix

The bug described in the issue above was fixed upstream: sarugaku/pip-shims#13.
It doesn't look like the pip-shims vendor was patched (nothing in tasks/vendoring/patches), so I simply ran pipenv run invoke vendoring.update --package="pip-shims==0.3.0".

The checklist

• Associated issue: pip 18.1 causes "TypeError: 'module' object is not callable" #2924
• A news fragment in the news/ directory to describe this fix with the extension .bugfix, .feature, .behavior, .doc. .vendor. or .trivial (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.

[techalchemy]

Thanks for the PR -- I know this is causing everyone some significant pain, but this will actually be upgraded by our vendoring tooling which automatically upgrades all of our dependencies. I already have a local branch with this change, I'm just finalizing some edge case fixes

[n6g7]

No problem, let me know if there's anythign I can do to help!