Update plug.md (#1154)
Update plug.md (#1154)

Replaced localhost with explicit 127.0.0.1
This works around a bug on some platforms
erickgnavar/elixir-school,psantos10/elixir-school,nscyclone/elixir-school,psantos10/elixir-school,nscyclone/elixir-school,doomspork/elixir-school,doomspork/elixir-school,nscyclone/elixir-school,erickgnavar/elixir-school,doomspork/elixir_school,erickgnavar/elixir-school,doomspork/elixir_school,nscyclone/elixir-school,psantos10/elixir-school,doomspork/elixir-school,doomspork/elixir_school