message: Fix rails example
diff: #### Option 1 - Asset pipeline
  Copy the compiled file
  -[`dist/client.js`](https://github.com/airbrake/airbrake-js/blob/master/dist/client.js)
  +[`dist/airbrake.esm.js`](https://github.com/airbrake/airbrake-js/blob/master/packages/browser/dist/airbrake.esm.js)
  from this repository to `vendor/assets/javascripts/airbrake.js` in your project.
  Then, add the following code to your Sprockets manifest:
  ```javascript
  -//= require @airbrake/browser
  +//= require airbrake
  var airbrake = new Airbrake.Notifier({
  projectId: 1,
  