Loading schemas from GitHub is broken

[happy5214]

The validator no longer seems to be able to download schemas that aren't bundled with the validator from GitHub. This error is an example:

ERROR: [SCHEMA_LOAD_FAILED] Could not load HED schema "{"nickname":"test","version":"3.0.0","library":"testlib","localPath":""}" from remote repository - "XMLHttpRequest is not defined". (For more information on this HED error, see https://hed-specification.readthedocs.io/en/latest/Appendix_B.html#schema-load-failed.)

XMLHttpRequest, which is basically AJAX, shouldn't even be in play here. I don't know what's going on.