add lesson translation fr/basics/mix-tasks (#493)
add lesson translation fr/basics/mix-tasks (#493)

* add lesson translation fr/basics/mix-tasks

* fix wording in fr/mix-tasks.md

huydx/elixir-school,nscyclone/elixir-school,doomspork/elixir_school,doomspork/elixir_school,erickgnavar/elixir-school,psantos10/elixir-school,doomspork/elixir-school,ElixirVietnam/elixir-school,nscyclone/elixir-school,doomspork/elixir-school,doomspork/elixir_school,nscyclone/elixir-school,ElixirVietnam/elixir-school,psantos10/elixir-school,erickgnavar/elixir-school,ElixirVietnam/elixir-school,nscyclone/elixir-school,huydx/elixir-school,psantos10/elixir-school,yuriibodarev/elixir-school,holsky/elixir-school,yuriibodarev/elixir-school,doomspork/elixir-school,yuriibodarev/elixir-school,erickgnavar/elixir-school,holsky/elixir-school,huydx/elixir-school,holsky/elixir-school