We are still on a version of pretender since 2017
https://github.com/pretenderjs/pretender/releases/tag/v1.6.1
Since then many changes have been made, including adding support
for xhr.upload. Upgrading will let us write proper acceptance
tests for uppy, which uses XmlHTTPRequest internally including
xhr.upload.
Updates pretender to 3.4.7 and fake-xml-http-request to 2.1.2.
Note: There have been no breaking changes in the releases that would
affect us, mainly dropping support for old node versions.
