`users` doesn't return packages where package is a test dependency

[glennmoy]

e.g. I know for a fact that AxisKeys is a test dependency for Impute.jl but it's not being listed here https://github.com/invenia/Impute.jl/blob/master/Project.toml#L38

julia> users("AxisKeys")
15-element Vector{String}:
 "AxisSets"
 "KeyedDistributions"

[mattBrzezinski]

Yeah... this only goes off of source code dependencies. Could add in an optional parameter to include test deps as well. Or just by default return back something like:

struct DependencyResults
  package_deps
  test_deps
end