Fix import to match pydocstyle v.1.1.0

[Nnonexistent]

After recent release of pydocstyle package prospector fails at import PEP257Checker.
This PR corrects import path.

[coveralls]

Coverage decreased (-0.1%) to 59.064% when pulling 6a934db on Nnonexistent:pydocstyle_import_fix into f89d998 on landscapeio:master.

[craSH]

I just ran across this issue as well, and thought I'd comment that this is the same change I'd have suggested in a PR.

$ pip freeze | grep -e prospector -e pydocstyle
prospector==0.12.2
pydocstyle==1.1.0

And from ipython in that environment:

In [1]: from pydocstyle.checker import PEP257Checker, AllError

In [2]: PEP257Checker
Out[2]: pydocstyle.checker.PEP257Checker

In [3]: AllError
Out[3]: pydocstyle.parser.AllError

[jamesdoherty]

For backwards compatibility, would it be worth importing from pydocstyle.checker first and then falling back to importing from pydocstyle if an ImportError is raised?

[carlio]

I agree that this approach is the better one to fixing the version, however I merged #190 and made a 0.12.3 release as I didn't have time to thoroughly test this approach yet. I will merge this once I make sure it will work and figure out backwards compatability issues too. Thanks for the really quick PR!

[coveralls]

Coverage increased (+0.07%) to 59.237% when pulling d42dc91 on Nnonexistent:pydocstyle_import_fix into 95e0981 on landscapeio:master.

[carlio]

Finally getting around to cleaning up various PRs and issues, sorry it took a while!