docs: tweak README (#201)

Author: okuryu

README.md

@@ -4,7 +4,6 @@ Serialize JavaScript
 Serialize JavaScript to a _superset_ of JSON that includes regular expressions, dates and functions.
 
 [![npm Version][npm-badge]][npm]
-[![Dependency Status][david-badge]][david]
 ![Test](https://github.com/yahoo/serialize-javascript/workflows/Test/badge.svg)
 
 ## Overview
@@ -143,10 +142,8 @@ See the [LICENSE file][LICENSE] for license text and copyright information.
 
 [npm]: https://www.npmjs.org/package/serialize-javascript
 [npm-badge]: https://img.shields.io/npm/v/serialize-javascript.svg?style=flat-square
-[david]: https://david-dm.org/yahoo/serialize-javascript
-[david-badge]: https://img.shields.io/david/yahoo/serialize-javascript.svg?style=flat-square
 [express-state]: https://github.com/yahoo/express-state
 [JSON.stringify]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify
 [LICENSE]: https://github.com/yahoo/serialize-javascript/blob/main/LICENSE
 [worker threads]: https://nodejs.org/api/worker_threads.html
-[closed-over variables]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Closures
+[closed-over variables]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Closures