Is your feature request related to a real problem or use-case?

It's a real problem to me; I prefer to spell this word as Falsy, not Falsey.

Describe a solution including usage in code example

Add the following to mapped-types.ts:

/**
 * Falsy
 * @desc Type representing falsy values in TypeScript: `null | undefined | false | 0 | ''`.
 * <br>Alias for `Falsey`
 * @example
 *   type Various = 'a' | 'b' | undefined | false;
 *
 *   // Expect: "a" | "b"
 *   Exclude<Various, Falsy>;
 */
export type Falsy = Falsey;

Who does this impact? Who is this for?

Spelling-sensitive users of this wonderful library such as myself 🙂

Describe alternatives you've considered (optional)

Have done this once or twice, but for obvious reasons it is annoying to do:

import { Falsey as Falsy } from 'utility-types';

Additional context (optional)

Falsy on MDN
Is it “falsy” or “falsey”?
“Falsy” vs “Falsey” – I’m Making the Call