fix: sort failures appropriately

[panva]

This makes sure failed items are not shown as fastest.

[ShogunPanda]

That's a good remark, thanks for noticing.
I think we can simplify this just by setting the mean of a failed items to 0 in https://github.com/ShogunPanda/cronometro/blob/master/src/index.ts#L23.
This way b.mean - a.mean holds a negative number for failed items.
What do you think?

[panva]

Sure. Feel free to close this is you want to go the other route.