Re-add missing Supervisor behaviour (#7288)
Re-add missing Supervisor behaviour (#7288)

Closes #7285.
gfvcastro/elixir,kimshrier/elixir,gfvcastro/elixir,ggcampinho/elixir,kelvinst/elixir,kimshrier/elixir,kelvinst/elixir,pedrosnk/elixir,michalmuskala/elixir,joshprice/elixir,ggcampinho/elixir,pedrosnk/elixir,lexmag/elixir,elixir-lang/elixir,lexmag/elixir