fix plug lesson (#1513)
fix plug lesson (#1513)


nscyclone/elixir-school,doomspork/elixir-school,nscyclone/elixir-school,nscyclone/elixir-school,doomspork/elixir-school,doomspork/elixir_school,nscyclone/elixir-school,doomspork/elixir_school,doomspork/elixir_school,doomspork/elixir-school