Fixed pep8 violations. Some 'line too long' errors still remain.

examples/applications/plot_species_distribution_modeling.py

examples/cluster/plot_adjusted_for_chance_measures.py

examples/cluster/plot_affinity_propagation.py

examples/cluster/plot_cluster_comparison.py

examples/cluster/plot_dbscan.py

examples/cluster/plot_dict_face_patches.py

examples/cluster/plot_digits_agglomeration.py

examples/cluster/plot_kmeans_digits.py

examples/cluster/plot_kmeans_stability_low_dim_dense.py

examples/cluster/plot_lena_segmentation.py

examples/cluster/plot_lena_ward_segmentation.py

examples/cluster/plot_mean_shift.py

examples/cluster/plot_mini_batch_kmeans.py

examples/covariance/plot_covariance_estimation.py

examples/covariance/plot_lw_vs_oas.py

examples/covariance/plot_robust_vs_empirical_covariance.py

examples/covariance/plot_sparse_cov.py

...s/cross_decomposition/plot_compare_cross_decomposition.py

examples/datasets/plot_random_dataset.py

examples/decomposition/plot_faces_decomposition.py