message: Refactor toCelsius
diff: -setup.toCelsius = function (temp) {
  +setup.toCelsius = temp => {
  if (settings.showCelsius) {
  console.log(`${temp} in Fahrenheit`)
  - temp -= 32
  - temp = `${Math.trunc(temp *= 0.5556)} degrees Celsius`
  + temp = Math.trunc((temp - 32) * 0.5556)
  console.log(`${temp} in Celsius`)
  - } else {
  - temp += ' degrees Fahrenheit'
  + return `${temp} degrees Celsius`
  }
  - return temp
  + return `${temp} degrees Fahrenheit`
  }
  