ci(release): 4.0.0 (#984)

Version bump in package.json and package-lock.json for release
[4.0.0](https://github.com/duffelhq/duffel-api-javascript/releases/tag/v4.0.0)

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@duffel/api",
-  "version": "3.3.0",
+  "version": "4.0.0",
   "description": "Javascript client library for the Duffel API",
   "main": "dist/index.js",
   "module": "dist/index.es.js",