Fix ModuleNotFoundError: No module named 'pandas.formats'

[cgohlke]

Fixes test_shim failure:

================================== FAILURES ===================================
__________________________________ test_shim __________________________________

    def test_shim():
        # https://github.com/pandas-dev/pandas/pull/16059
        # Remove in 0.21
        with tm.assert_produces_warning(FutureWarning,
                                        check_stacklevel=False):
>           from pandas.formats.style import Styler as _styler  # noqa
E           ModuleNotFoundError: No module named 'pandas.formats'

X:\Python36\lib\site-packages\pandas\tests\io\formats\test_style.py:866: ModuleNotFoundError

[codecov]

Codecov Report

Merging #16239 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #16239      +/-   ##
==========================================
- Coverage   90.24%   90.23%   -0.01%     
==========================================
  Files         164      164              
  Lines       50894    50894              
==========================================
- Hits        45930    45926       -4     
- Misses       4964     4968       +4

Flag	Coverage Δ
#multiple	88.02% <ø> (ø)	⬆️
#single	40.3% <ø> (-0.1%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.58% <0%> (-0.1%)	⬇️
pandas/_version.py	44.65% <0%> (+1.9%)	⬆️

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[TomAugspurger]

Thanks for catching this!