Improve error message on invalid use of Supervisor.Spec
Improve error message on invalid use of Supervisor.Spec

Closes #6407

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