Update type definition of last

[deiga]

last would return undefined if input is an array of length 0, but this is not reflected in the type definition

[selfrefactor]

Txs for spotting this. I did merge it to master, but I need to add more changes before making a release. I will update once release is made.

[selfrefactor]

I added the comment about 0 length, but the change that will be in next version is a bit different. Still, the end result is the same:

it('empty array', () => {
    const list = [] as const
    head(emptyList) // $ExpectType undefined
    head(list) // $ExpectType undefined
    last(emptyList) // $ExpectType undefined
    last(list) // $ExpectType undefined
  })

I will inform when it is released.