Add leap year label

[nicolasmartinez0510]

Something that would be cool to have is a label next to date navigation to indicate if that year is leap year. Like this:

<span className='nice-dates-navigation_current'>
        {format(month, getYear(month) === getYear(new Date()) ? 'LLLL' : 'LLLL yyyy', { locale })}
        <span className="nice-dates-navigation_current_leap-year">{ isLeapYear(month) ? ' (Leap Year) ' : '' }</span>
</span>

obviously to do this need to add the internationalization(of course if you want to do this )