Change truncate naive date time fn to be Elixir 1.5 compatible for heroku

[Cleop]

Our current display of the date/time that a comment is written uses truncate which is from Elixir 1.6. As heroku uses v.1.5 we need to change this so that it is compatible.

Initial solution:

 def format_date(date) do
    date
    |> NaiveDateTime.to_iso8601
    |> tidyISODate
  end

  def tidyISODate(iso_date) do
    iso_date
    |> String.replace("T", " ")
    |> String.split(".")
    |> List.first
  end

[nelsonic]

looks good. 👍