IssuedAt claim is not verified when jwt.WithIssuedAt() option is given to Parser

In jwt/validator.go, the validation logic for IssuedAt is:

	// Check issued-at if the option is enabled
	if v.verifyIat {
		if err = v.verifyIssuedAt(claims, now, false); err != nil {
			errs = append(errs, err)
		}
	}

Because the last parameter to v.verifyIssuedAt(claims, now, false) is false, IssuedAt is not verified even if v.verifyIat is true.

The correct logic is to use v.verifyIssuedAt(claims, now, true).