Update changeset validation notes (#2618)
Update changeset validation notes (#2618)

Adding the atom `:age` to the code example making it easier to follow that it's talking about the same changeset made above, not creating a second changeset for validation.
doomspork/elixir_school,doomspork/elixir-school,doomspork/elixir_school,doomspork/elixir-school,doomspork/elixir-school,doomspork/elixir_school