Fix by adding comment when executing make test that send

The build onTravis do not use Pylint and do not raise errors.
When executing locally `make test`, pylint complains about: 
```
"FAIL: test/test_distance.py:6 | E0611 no-name-in-module:  No name 'assert_raises' in module 'nose.tools'"
```
See for a fix <http://blog.daniel-watkins.co.uk/2013/09/fixing-nosetools-pylint-errors.html>
I choose the option to comment for ignoring the E0611 error or more refactoring with `unittest.TestCase` would be required
e.g <https://stackoverflow.com/questions/10716506/where-is-noses-assert-raises-function> whereas `nose.tools` approach is valid IMO.