display code for error exercise

[valentina-s]

In the novice-inflammation lesson we decided to display the code producing the different types of errors, so students easily look into the code and identify the error (without dealing with extra files errors_01.py, errors_02.py):
swcarpentry/python-novice-inflammation#51

In the gapminder there is similar exercise in 15-scope lesson. If you are interested in such a change we can submit a PR. The code of the function might help the user understand the key error, but is not relevant to the other questions. Let us know what you think.

[alee]

Sorry for the delayed response @valentina-s - I think this would be a great idea if you could send us a PR! If I understand correctly the PR would be adding the error generating code inline with the lesson template so there wouldn't be references to /Users/ghopper/foo.py etc?