See https://github.com/JuliaLang/Pkg.jl/issues/601, https://github.com/JuliaLang/Pkg.jl/pull/634 and https://github.com/JuliaLang/Pkg.jl/issues/790
The fix will be included in Julia v1.0.2, but you can fix the problem by just deleting the .DS_Store file.