Restore Snyk badge and switch license badge to npm endpoint

Snyk's public test endpoint is serving the badge SVG again, so the
badge can come back. The license badge now reads from npm's license
field (more reliable than github/license detection) and links to a
relative LICENSE path so it resolves correctly on both GitHub and npm.

Author: jjxxs

README.md

@@ -19,7 +19,8 @@ A <b>WebSocket</b> for browsers with <b>auto-reconnect</b> and <b>message buffer
 
 [![npm version](https://img.shields.io/npm/v/websocket-ts.svg)](https://www.npmjs.org/package/websocket-ts)
 [![Bundle Size](https://deno.bundlejs.com/badge?q=websocket-ts@2.2.1)](https://bundlejs.com/?q=websocket-ts)
-[![License](https://img.shields.io/github/license/jjxxs/websocket-ts)](/LICENSE)
+[![Snyk security](https://snyk.io/test/npm/websocket-ts/badge.svg)](https://snyk.io/test/npm/websocket-ts)
+[![License](https://img.shields.io/npm/l/websocket-ts)](LICENSE)
 
 </div>