Review https://github.com/jupyterhub/nbgitpuller/pull/359

[yuvipanda]

jupyterhub/nbgitpuller#359 has been sitting for a bit, and it would be a great way to jump start our structured upstream OSS contribution process. It's a simple start because:

1. There's a clear bug report of a specific problem
2. The PR has a clear and veriiable fix that is possible to test

Suggested Steps

These are purely suggested steps, and need not be followed. Our goal is to see if this PR improves the project, and

1. Setup a local dev environment of nbgitpuller
2. Validate the error reported in Status page broken jupyterhub/nbgitpuller#358
3. Pull Update style-sheet links to reflect those from jupyter-server jupyterhub/nbgitpuller#359 and test to see if that fixes the issue
4. ??? We have to figure it out from here collectively :) Use your best judgement and ask questions!

Definition of done

• The PR had been responded to in some way
• We write down what we learnt from this process in Round 1: Strategic upstream OSS contributions #5058

[sgibson91]

@agoose77 and I completed this today