DOC: Fix contradicting KPSS-statistics interpretations in stationarity_detrending_adf_kpss.ipynb

[mzietlow]

• closes DOC: KPSS interpretation in stationarity_detrending_adf_kpss.ipynb  #7089
• code/documentation is well formatted.
• properly formatted commit message. See
  NumPy's guide.

Details

Notes:

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[bashtage]

Perfect. Thanks.

[coveralls]

Coverage remained the same at 88.408% when pulling fa9f348 on mzietlow:DOC_contradicting_KPSS_interpretations into dc9d80a on statsmodels:master.