Fix docs for the [test_coverage] option of the [mix test]
Fix docs for the [test_coverage] option of the [mix test]

pedrosnk/elixir,lexmag/elixir,gfvcastro/elixir,ggcampinho/elixir,antipax/elixir,kimshrier/elixir,elixir-lang/elixir,kelvinst/elixir,antipax/elixir,beedub/elixir,ggcampinho/elixir,joshprice/elixir,michalmuskala/elixir,kimshrier/elixir,lexmag/elixir,pedrosnk/elixir,gfvcastro/elixir,kelvinst/elixir,beedub/elixir