add circleCI badge

Author: JakubNer

README.md

@@ -3,6 +3,7 @@
 # ledgers.js
 
 [![npm version](https://badge.fury.io/js/ledgers.js.svg)](https://badge.fury.io/js/ledgers.js)
+[![CircleCI](https://circleci.com/gh/overhide/ledgers.js.svg?style=svg)](https://circleci.com/gh/overhide/ledgers.js)
 
 [This repository](https://github.com/overhide/ledgers.js) is the [distribution](https://www.npmjs.com/package/ledgers.js) of the *ledgers.js* library ([source](https://github.com/overhide/ledgers.js/blob/master/src/ledgers.js))([API](https://overhide.github.io/ledgers.js/ledgers.js-rendered-docs/index.html)) in support of [ledger-based authorization](https://github.com/overhide/ledgers.js/blob/master/why/why.md).
 

dist/ledgers.js.map

@@ -2,6 +2,9 @@
   "name": "ledgers.js",
   "version": "2.0.0",
   "description": "JavaScript library for ledger-based authorizations :: abstracting different ledgers to be used in an application's authentication and authorization workflows.",
+  "engines": {
+    "node": "10.13.0"
+  },
   "main": "dist/ledgers.js",
   "repository": {
     "type": "git",