Fix typo in deriving docs
Fix typo in deriving docs

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