chore: Update CI status badge. (#52)

Author: kinyoklion

README.md

@@ -1,7 +1,7 @@
 # LaunchDarkly Client-Side SDK for Node.js
 
 [![NPM](https://img.shields.io/npm/v/launchdarkly-node-client-sdk.svg?style=flat-square)](https://www.npmjs.com/package/launchdarkly-node-client-sdk)
-[![CircleCI](https://circleci.com/gh/launchdarkly/node-client-sdk.svg?style=svg)](https://circleci.com/gh/launchdarkly/node-client-sdk)
+[![Build and Test](https://github.com/launchdarkly/node-client-sdk/actions/workflows/ci.yml/badge.svg)](https://github.com/launchdarkly/node-client-sdk/actions/workflows/ci.yml)
 [![Documentation](https://img.shields.io/static/v1?label=GitHub+Pages&message=API+reference&color=00add8)](https://launchdarkly.github.io/node-client-sdk)
 
 The LaunchDarkly Client-Side SDK for Node.js is designed primarily for use by code that is deployed to an end user, such as in a desktop application or a smart device. It follows the client-side LaunchDarkly model for single-user contexts (much like our mobile or JavaScript SDKs). It is not intended for use in multi-user systems such as web servers and applications.