`mix deps.get --only docs` in `coveralls.sh`

[kianmeng]

I've noticed that in coveralls.sh, the script only pull dependencies for :docs environment:

echo "Posting coveralls"
mix deps.get --only docs
mix coveralls.travis

But in mix.exs, there is no deps set for :docs environment:

 defp deps do
   [
     {:optimus, "~> 0.1.11"},
     {:dialyxir, "~> 1.0.0-rc.7", only: [:dev, :test], runtime: false},
     {:excoveralls, "~> 0.11", only: :test},
     {:excoveralls_linter, "~> 0.0.1", only: :test},
     {:ex_doc, ">= 0.0.0", only: :dev, runtime: false},
     {:earmark, "~> 1.4", only: :dev, runtime: false}
   ]
 end

Is this intentional or it's a bug?