I'm trying to use https://github.com/siddharthkp/bundlesize which depends on this library in Github Enterprise.

Looking at the code

    url: `https://api.github.com/repos/${build.repo}/statuses/${build.sha}`,

Should be(in my case):

    url: `https://github.ibm.com/api/v3/repos/${build.repo}/statuses/${build.sha}`,

You can probably accept another parameter in the constructor with the GitHub API URL.
I have also seen people using environment variables like: GITHUB_API.

Thanks for the great work you are doing.