Allow leaving an empty value

[Richienb]

For example:

await pMap(["example.com", "notawebsite.invalid", "google.com"], async url => {
	try {
		return await got(url)
	} catch {
		return pMap.hole()
	}
})
//=> ["<example.com contents>", "<google.com contents>"]

[sindresorhus]

Do you actually want a whole? Holes in arrays are usually discouraged. How about pMap.skip instead?