Fixed showing colors when using `yarn dev:debug`
Fixed showing colors when using `yarn dev:debug`

- because we use `concurrently`, `debug` thinks it's not inside a TTY,
  so it doesn't show colors
- we can force it to show colors using the DEBUG_COLORS env variable, as
  done in this commit

TryGhost/Ghost,TryGhost/Ghost,TryGhost/Ghost