Fix example

  >>> featurizers = dc.feat.CoulombMatrixEig(max_atoms=23)

  >>> input_file = 'deepchem/feat/tests/data/water.sdf' # really backed by water.sdf.csv

  >>> tasks = ["atomization_energy"]

  >>> featurizer = dc.data.SDFLoader(tasks, smiles_field="smiles", mol_field="mol",

  ...                                    featurizer=featurizers, verbose=False)

  >>> featurizer = dc.data.SDFLoader(tasks, featurizer=featurizers)

  >>> dataset = featurizer.featurize(input_file)

  Reading structures from deepchem/feat/tests/data/water.sdf.

  Featurizing sample 0