Fix typo in `examples/compose/plot_column_transformer.py`

* tag '0.20.0': (77 commits)
  ColumnTransformer generalization to work on empty lists (scikit-learn#12084)
  add sparse_threshold to make_columns_transformer (scikit-learn#12152)
  [MRG] Convert ColumnTransformer input list to numpy array (scikit-learn#12104)
  Change version to 0.20.0
  BUG: check equality instead of identity in check_cv (scikit-learn#12155)
  [MRG] Fix FutureWarnings in logistic regression examples (scikit-learn#12114)
  [MRG] Update test_metaestimators to pass y parameter when calling score (scikit-learn#12089)
  DOC Removed duplicated doc in tree.rst (scikit-learn#11922)
  [MRG] DOC covariance doctest examples (scikit-learn#12124)
  typo and formatting fixes in 0.20 doc (scikit-learn#11963)
  DOC Replaced the deprecated early_stopping parameter with n_iter_no_change. (scikit-learn#12133)
  [MRG +1] ColumnTransformer: store evaluated function column specifier during fit (scikit-learn#12107)
  Fix typo (scikit-learn#12126)
  DOC Typo in OneHotEncoder
  DOC Update fit_transform docstring of OneHotEncoder (scikit-learn#12117)
  DOC Removing quotes from variant names. (scikit-learn#12113)
  DOC BaggingRegressor missing default value for oob_score in docstring (scikit-learn#12108)
  [MRG] MNT Re-enable PyPy CI (scikit-learn#12039)
  MNT Only checks warnings on latest depedendencies versions in CI (scikit-learn#12048)
  TST Ignore warnings in common test to avoid collection errors (scikit-learn#12093)
  ...

* releases: (77 commits)
  ColumnTransformer generalization to work on empty lists (scikit-learn#12084)
  add sparse_threshold to make_columns_transformer (scikit-learn#12152)
  [MRG] Convert ColumnTransformer input list to numpy array (scikit-learn#12104)
  Change version to 0.20.0
  BUG: check equality instead of identity in check_cv (scikit-learn#12155)
  [MRG] Fix FutureWarnings in logistic regression examples (scikit-learn#12114)
  [MRG] Update test_metaestimators to pass y parameter when calling score (scikit-learn#12089)
  DOC Removed duplicated doc in tree.rst (scikit-learn#11922)
  [MRG] DOC covariance doctest examples (scikit-learn#12124)
  typo and formatting fixes in 0.20 doc (scikit-learn#11963)
  DOC Replaced the deprecated early_stopping parameter with n_iter_no_change. (scikit-learn#12133)
  [MRG +1] ColumnTransformer: store evaluated function column specifier during fit (scikit-learn#12107)
  Fix typo (scikit-learn#12126)
  DOC Typo in OneHotEncoder
  DOC Update fit_transform docstring of OneHotEncoder (scikit-learn#12117)
  DOC Removing quotes from variant names. (scikit-learn#12113)
  DOC BaggingRegressor missing default value for oob_score in docstring (scikit-learn#12108)
  [MRG] MNT Re-enable PyPy CI (scikit-learn#12039)
  MNT Only checks warnings on latest depedendencies versions in CI (scikit-learn#12048)
  TST Ignore warnings in common test to avoid collection errors (scikit-learn#12093)
  ...

* dfsg: (77 commits)
  ColumnTransformer generalization to work on empty lists (scikit-learn#12084)
  add sparse_threshold to make_columns_transformer (scikit-learn#12152)
  [MRG] Convert ColumnTransformer input list to numpy array (scikit-learn#12104)
  Change version to 0.20.0
  BUG: check equality instead of identity in check_cv (scikit-learn#12155)
  [MRG] Fix FutureWarnings in logistic regression examples (scikit-learn#12114)
  [MRG] Update test_metaestimators to pass y parameter when calling score (scikit-learn#12089)
  DOC Removed duplicated doc in tree.rst (scikit-learn#11922)
  [MRG] DOC covariance doctest examples (scikit-learn#12124)
  typo and formatting fixes in 0.20 doc (scikit-learn#11963)
  DOC Replaced the deprecated early_stopping parameter with n_iter_no_change. (scikit-learn#12133)
  [MRG +1] ColumnTransformer: store evaluated function column specifier during fit (scikit-learn#12107)
  Fix typo (scikit-learn#12126)
  DOC Typo in OneHotEncoder
  DOC Update fit_transform docstring of OneHotEncoder (scikit-learn#12117)
  DOC Removing quotes from variant names. (scikit-learn#12113)
  DOC BaggingRegressor missing default value for oob_score in docstring (scikit-learn#12108)
  [MRG] MNT Re-enable PyPy CI (scikit-learn#12039)
  MNT Only checks warnings on latest depedendencies versions in CI (scikit-learn#12048)
  TST Ignore warnings in common test to avoid collection errors (scikit-learn#12093)
  ...