julia> Pkg.add(PackageSpec(url="https://github.com/JuliaML/OpenAIGym.jl", rev="master"))
Updating git-repo `https://github.com/JuliaML/OpenAIGym.jl`
Resolving package versions...
ERROR: Unsatisfiable requirements detected for package Reinforce [0376cc21]:
Reinforce [0376cc21] log:
├─possible versions are: [0.0.1, 0.1.0, 0.2.0] or uninstalled
├─restricted to versions 0.1.0-0.1 by OpenAIGym [41d6fcb8], leaving only versions 0.1.0
│ └─OpenAIGym [41d6fcb8] log:
│ ├─possible versions are: 0.1.0 or uninstalled
│ └─OpenAIGym [41d6fcb8] is fixed to version 0.1.0
└─restricted by julia compatibility requirements to versions: 0.2.0 or uninstalled — no versions left