Fix Artifacts on Julia versions <1.6

As of 1.6 Artifacts is now in Julia base, need to find a workaround for versions before this using Pkg.Artifacts. Currently any version <1.6 will fail. 

Also Pkg.Artifacts requires at least 1.3 (https://pkgdocs.julialang.org/v1/artifacts/) so need to remove support for anything less than that. 