scipy.sparse.csr DeprecationWarning in user_output.py

[jGaboardi]

We are hitting a DeprecationWarning thrown by scipy.sparse in user_output.py:

spreg/user_output.py:15: DeprecationWarning: Please use `csr_matrix` from the `scipy.sparse` namespace, the `scipy.sparse.csr` namespace is deprecated.
    from scipy.sparse.csr import csr_matrix

Simply need to adjust the import structure.

[pedrovma]

Part of issue #126.