Jin

Results 2 issues of Jin

### Description According to [the docs](https://www.w3schools.com/js/js_variables.asp), using `var` is not recommended, unless it's necessary, It would be useful to replace `var` in `index.js` with `let` or `const` depending on their...

future

This PR is created to handle the [issue #112](https://github.com/expressjs/cookie-parser/issues/112) This PR is to replace `var` with `let` and `const` in `index.js` file and `README.md` file.

future