v1.3.1 -- bumping docfx to v2.57.2

⚠️ Note -- there was a faulty v1.3.0 release which we un-published.
(Ed: note -- sorry about that v1.3.0, folks! Something went wrong with my local push to dockerhub. - @SeanKilleen).

v1.2.0 -- bumping docfx to v2.57.1

Merge pull request #3 from nunit/update-docfx-build

Update docfx build version from 2.56.1 --> 2.57.1

v1.1.0

This release updates the docfx version to 2.56.1.