Fixed incredibly minor spelling mistake
Merge pull request #2840 from earino/develop

DOC Fixed minor spelling mistake
Added a method for computing the manhattan_distances between two sparse matrices to sklearn.pairwise.pairwise_fast.pyx
Modified sklearn.metrics.pairwise.manhattan_distances to work with sparse matrices.
Modified function docstring for sklearn.metrics.pairwise.manhattan_distances to have information about using the function with sparse matrices.
Added a test to check that sklearn.metrics.pairwise.manhattan_distances handles combinations of sparse input matrices correctly, i.e. converts them to coo matrices.