Can add package in Julia terminal, but not in Juno or Jupyter

[Helveg]

Hello,

I executed this command succesfully about half a year ago on my Windows 7 machine: Pkg.add("Plots") in the terminal of a Julia installation. Now I wanted to start using an IDE and first tried Atom. To my surprise it turned out it uses a different Julia environment because the Plots package wasn't installed here. When I enter the Pkg.add("Plots") I get the following error:
julia> Pkg.add("Plots") INFO: Cloning cache of PlotThemes from https://github.com/JuliaPlots/PlotThemes.jl.git ERROR: Cannot clone PlotThemes from https://github.com/JuliaPlots/PlotThemes.jl.git. user cancelled certificate check: prefetch(::String, ::String, ::Array{String,1}) at .\pkg\cache.jl:56 resolve(::Dict{String,Base.Pkg.Types.VersionSet}, ::Dict{String,Dict{VersionNumber,Base.Pkg.Types.Av ailable}}, ::Dict{String,Tuple{VersionNumber,Bool}}, ::Dict{String,Base.Pkg.Types.Fixed}, ::Dict{Str ing,VersionNumber}, ::Set{String}) at .\pkg\entry.jl:516 resolve(::Dict{String,Base.Pkg.Types.VersionSet}, ::Dict{String,Dict{VersionNumber,Base.Pkg.Types.Av ailable}}, ::Dict{String,Tuple{VersionNumber,Bool}}, ::Dict{String,Base.Pkg.Types.Fixed}) at .\pkg\e ntry.jl:479 edit(::Function, ::String, ::Base.Pkg.Types.VersionSet, ::Vararg{Base.Pkg.Types.VersionSet,N} where N) at .\pkg\entry.jl:30 (::Base.Pkg.Entry.##1#3{String,Base.Pkg.Types.VersionSet})() at .\task.jl:335

The same happens when I try to execute it in a Jupyter notebook. I'm not sure if it's Plots related per se but I'd have no idea where else to ask this question. Is this firewall or Windows related? Any suggestion on things I could try?

[Helveg]

It was a duplicate of the issue JuliaLang/julia#26167