Fix awaiting change handlers before closing

[KevinLHansen]

This has proven to be an issue for us when we need to do long-running tasks when reacting to change events (specifically, we make an HTTP request when the range changes). Consider the following:

Razor:

<DateRangePicker OnRangeSelect=RangeChanged />

C#:

private async Task RangeChanged(DateRange range)
{
    _Range = range;
    await Save();
}

private async Task Save()
{
   // simulated work
    await Task.Delay(1000);
}

In this example, the selector will only close after 1000ms, whereas it makes more sense UX-wise to close immediately

[KevinLHansen]

@jdtcn Could you take a look at this? :)

[jdtcn]

Hi, thanks for the fix, I will release a new version that will include it soon