valueOf with specific unitOfTime

[NinjaDev06]

I would like to get the duration of the range in any formats not only in milliseconds. The method valueOf may received unitOfTime.Base as a parameter.

Example

const start = moment('2011-04-15', 'YYYY-MM-DD');
const end   = moment('2011-04-16', 'YYYY-MM-DD');
const range = moment.range(start, end);

const hours = range.valueOf('hours'); // 24
const days = range.valueOf('days'); // 1