fix(addRule): allow add return undefined

[MarvelSQ]

当前addRule要求返回boolean 或 ErrorMessage

Schema.Types.StringType().addRule(value => {
  // empty
});

而代码中的逻辑是 返回 false 或 ErrorMessage 进行处理，没有返回值会被认为是通过的
所以对应的类型声明应允许返回空

[simonguo]

Error: Errors in typescript@local for external dependencies:
Error: ../src/utils/createValidatorAsync.ts(24,9): error TS2345: Argument of type '(checkResult: CheckResult<E> | boolean) => CheckResult<E> | null' is not assignable to parameter of type '(value: boolean | CheckResult<E> | undefined) => CheckResult<E> | PromiseLike<CheckResult<E> | null> | null'.
  Types of parameters 'checkResult' and 'value' are incompatible.
    Type 'boolean | CheckResult<E> | undefined' is not assignable to type 'boolean | CheckResult<E>'.
      Type 'undefined' is not assignable to type 'boolean | CheckResult<E>'.

    at /home/runner/work/schema-typed/schema-typed/node_modules/dtslint/bin/index.js:206:19
    at Generator.next (<anonymous>)
    at fulfilled (/home/runner/work/schema-typed/schema-typed/node_modules/dtslint/bin/index.js:6:58)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! schema-typed@2.0.2 test:types: `dtslint --expectOnly --localTs node_modules/typescript/lib types`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the schema-typed@2.0.2 test:types script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/runner/.npm/_logs/2021-12-09T05_49_18_190Z-debug.log
npm ERR! Test failed.  See above for more details.