Issue with fetching last commit

[NoahTheDuke]

Seems that the params={'sha': 'main'}, line can make fetching the commits not work.

Current behavior

$ changelog mtgred netrunner
Traceback (most recent call last):
  File "/Users/noah/.pyenv/versions/3.7.5/bin/changelog", line 8, in <module>
    sys.exit(main())
  File "/Users/noah/.pyenv/versions/3.7.5/lib/python3.7/site-packages/changelog/__init__.py", line 232, in main
    changelog = generate_changelog(**vars(args))
  File "/Users/noah/.pyenv/versions/3.7.5/lib/python3.7/site-packages/changelog/__init__.py", line 195, in generate_changelog
    prs = fetch_changes(github_config, owner, repo, previous_tag, current_tag)
  File "/Users/noah/.pyenv/versions/3.7.5/lib/python3.7/site-packages/changelog/__init__.py", line 155, in fetch_changes
    current_commit = get_last_commit(github_config, owner, repo, branch)
  File "/Users/noah/.pyenv/versions/3.7.5/lib/python3.7/site-packages/changelog/__init__.py", line 84, in get_last_commit
    commits_json['message']))
changelog.GitHubError: Unable to get commits. Not Found

Expected behavior

$ changelog mtgred netrunner
- Noise milling fix #5348
[other commits here as well]

Steps to replicate behavior (include URLs)

The only thing I changed to get this working is line 79 of init.py:

    commits_response = requests.get(commits_url, #params={'sha': 'main'},
                                    headers=github_config.headers)

I don't know enough to know why this works, just that it does.

Thanks so much.