Building fonts on linux fails

[sonulohani]

Problem description
I went through README.md and tried building the fonts from source, however I am getting error while building python dependencies. Here is the error screenshot:

Seems like the package is meant to be used only in macOs. The package is downloaded as part of drawbot dependencies.

Expected behavior
No error should be reported when building for linux unless it is unsupported.

To Reproduce
Steps to reproduce the behavior:

1. Go to README.md
2. Follow steps under build instructions
3. See the error in linux after running pip install -U -r requirements.txt

Environment (please complete the following information):

• OS: Ubuntu 20.04