julia-git error on NixOS

julia.log

  _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.5.0-dev
 _/ |\__'_|_|_|\__'_|  |  
|__/                   |  x86_64-unknown-linux-gnu

julia> Pkg.add("JSON")
INFO: Initializing package repository /home/nixo/.julia/v0.5
INFO: Cloning METADATA from https://github.com/JuliaLang/METADATA.jl
ERROR: GitError(Code:ECERTIFICATE, Class:SSL, The SSL certificate is invalid)
 [inlined code] from ./libgit2/error.jl:98
 in clone(::ASCIIString, ::ASCIIString, ::Base.LibGit2.CloneOptions) at ./libgit2/repository.jl:189
 in #clone#102(::ASCIIString, ::Bool, ::Ptr{Void}, ::Nullable{Base.LibGit2.AbstractPayload}, ::Any, ::ASCIIString, ::ASCIIString) at ./libgit2.jl:310
 [inlined code] from ./boot.jl:331
 in (::Base.Pkg.Dir.##4#6{ASCIIString,ASCIIString})() at ./pkg/dir.jl:49
 in cd(::Base.Pkg.Dir.##4#6{ASCIIString,ASCIIString}, ::ASCIIString) at ./file.jl:47
 in init(::ASCIIString, ::ASCIIString) at ./pkg/dir.jl:47
 in #cd#1(::Array{Any,1}, ::Any, ::Any, ::ASCIIString, ::Vararg{ASCIIString}) at ./pkg/dir.jl:35
 [inlined code] from ./boot.jl:331
 in add(::ASCIIString) at ./pkg.jl:83
 in eval(::Module, ::Any) at ./boot.jl:267