Strip ANSI color codes in non-TTY mode
Strip ANSI color codes in non-TTY mode

When running `mix release` non-interactively, for example as part of a script,
we should not see color codes mixed with the output. This can be tested by
piping the output of mix.release. E.g.:

  # Colors visible:
  mix release

  # No colors
  mix release | cat

GalaxyGorilla/exrm,bitwalker/exrm