example fixes to clean first docstring paragraph of rst code

examples/applications/plot_stock_market.py

examples/cluster/plot_segmentation_toy.py

examples/cluster/plot_ward_structured_vs_unstructured.py

examples/covariance/plot_covariance_estimation.py

examples/covariance/plot_mahalanobis_distances.py

examples/covariance/plot_outlier_detection.py

examples/datasets/plot_digits_last_image.py

examples/decomposition/plot_ica_blind_source_separation.py

examples/decomposition/plot_ica_vs_pca.py

examples/decomposition/plot_image_denoising.py

examples/exercises/plot_cv_diabetes.py

examples/exercises/plot_cv_digits.py

examples/exercises/plot_digits_classification_exercise.py

examples/exercises/plot_iris_exercise.py

examples/grid_search_digits.py

examples/linear_model/plot_ard.py

examples/linear_model/plot_bayesian_ridge.py

examples/linear_model/plot_ridge_path.py

examples/linear_model/plot_sgd_loss_functions.py

examples/linear_model/plot_sgd_penalties.py