* Travis CI: Add pytest --doctest-modules neural_network
Fixes#987
```
neural_network/perceptron.py:123: in <module>
sample.insert(i, float(input('value: ')))
../lib/python3.7/site-packages/_pytest/capture.py:693: in read
raise IOError("reading from stdin while output is captured")
E OSError: reading from stdin while output is captured
-------------------------------------------------------------------------------- Captured stdout --------------------------------------------------------------------------------
('\nEpoch:\n', 399)
------------------------
value:
```
* Adding fix from #1056 -- thanks @QuantumNovice
* if __name__ == '__main__':
* pytest --ignore=virtualenv # do not test our dependencies
