bugfix 729 main_v3.1 fix SyntaxError use case doc

[georgemccabe]

Pull Request Testing

• Describe testing already performed for these changes:
  
  Verified that the title for this use case is no longer SyntaxError:

dtcenter.github.io/METplus/latest/generated/model_applications/medium_range/TCStat_SeriesAnalysis_fcstGFS_obsGFS_FeatureRelative_SeriesByLead_PyEmbed_IVT.html#sphx-glr-generated-model-applications-medium-range-tcstat-seriesanalysis-fcstgfs-obsgfs-featurerelative-seriesbylead-pyembed-ivt-py

• Recommend testing for the reviewer to perform, including the location of input datasets:
  
  Scan docs for anything incorrect/broken

• Will this PR result in changes to the test suite? [No]
  
  If yes, describe the new output and/or changes to the existing output:
  

• After merging, should the reviewer DELETE the feature branch from GitHub? [Yes]
  

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[JohnHalleyGotway]

Looks fine to me. I don't see any more syntax errors in the docs. And the changes are confined to documentation and comments.