modify (translate) {
      const gap = Components.Gaps.value
      const width = Components.Sizes.width
      const focusAt = Glide.settings.focusAt
      const slideWidth = Components.Sizes.slideWidth

      if (focusAt === 'center') {
        return translate - (width / 2 - slideWidth / 2)
      }

      return translate - (slideWidth * focusAt) - (gap * focusAt)
    }
Modifies passed translate value with index in the `focusAt` setting.

@param  {Number} translate
@return {Number}