fix: add optional message to nonNullable schema methods

[ranquild]

Fixes #2069

Adds an optional msg?: Message argument to nonNullable method on every schema object. The argument is already supported by the base Schema class, and we only need to pass it properly with TypeScript.

Also updates nullable and nonNullable signatures in README.md.

[ranquild]

@jquense could you take a look, please?

[lmarvaud]

Hello,

It seem that the typing of "notNullable" and "nullable" had been swaped. In Schema.ts, inherited by few validators, only nonNullable takes a parameter.

yup/src/schema.ts

Lines 710 to 715 in 5db2b2f

	nullable(): any {
	return this.nullability(true);
	}
	nonNullable(message = locale.notNull): any {
	return this.nullability(false, message);
	}

Actually wouldn't it be cleaner to add those types in the Schema interface, to avoid code duplication and those type of error ?

[jquense]

thanks!