Add environment variable check

[arun-ghontale]

The autograder being used in XCS224U when converting the notebook hw_colors.ipynb to a python script adds get_ipython() command to the script. This won't work unless you import it - from IPython import get_ipython. something like this:

So it would be good to change these lines of code from:

to this:

I already have the permission to make changes to the repo. Just wanted to run by you once before making changes and committing it. Thanks @cgpotts

[cgpotts]

@arun-ghontale That change seems fine; free free to push changes! I'm glad to know that this is a potential issue too. Thanks!