npm: Set package's type to module

This ensure NodeJS treats all JS files as ES6 modules.

See https://nodejs.org/api/esm.html#esm_code_package_json_code_code_type_code_field

Author: korya

package.json

@@ -4,6 +4,7 @@
   "license": "MIT",
   "homepage": "https://github.com/PlanitarInc/msg-switch",
   "main": "src/index.js",
+  "type": "module",
   "sideEffects": false,
   "scripts": {
     "serve": "vue-cli-service serve",