docs: running the test suite, sm.discrete.test() not available

[jkornblum]

I've been browsing through the developer docs found an example that does not work.

On http://www.statsmodels.org/stable/dev/test_notes.html#running-the-test-suite page

It says you can run test sub-modules with sm.discrete.test() which throws an error AttributeError: module 'statsmodels.api' has no attribute 'discrete'

I see that statsmodels.api does not import .discrete directely but imports classes inside of discrete.