They're taking a long time to release 2.4.1 and it's only a few commits,
we need one of them.
Also use the NS1.x binaries instead so 2018-xx branches which don't build
netstandard.dll for monodroid etc can use it.
In fact, xunit removed the NS2.0 binaries again in 2.4.1 so we don't even have much choice :)