Fix #427

[chris-clem]

Reference Issues/PRs

Fixes #427

Pull Request Checklist

• [ ] Added a note about the modification or contribution to the ./CHANGELOG.md file (if applicable)
• [x] Added appropriate unit test functions in the ./graphein/tests/* directories (if applicable)
• [ ] Modify documentation in the corresponding Jupyter Notebook under ./notebooks/ (if applicable)
• [x] Ran python -m py.test tests/ and make sure that all unit tests pass (for small modifications, it might be sufficient to only run the specific test file, e.g., python -m py.test tests/protein/test_graphs.py)
• [x] Checked for style issues by running black . and isort .