Staticman Invitation is Case Sensitive

A recent invitation error under Staticman v3

HTML and URL links are case insensitive. For example, GOOGLE.COM and give the same address. As a result, after creating my fork of Beautiful Jekyll, I invited @staticmanlab to join my GitHub repo by firing the URL

but I got

After matching vincenttam with the case of my user name displayed in the link for each of GitHub repos,
github collaborator

Collaborator successfully added

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