Fastboot + RESTAdapter and Error: Ember Data Request 401

@kratiahuja @tomdale

Hope you're doing well.

I need you assistance in the below case.

I am using RESTAdapter for APIs. Unfortunately I am facing issue with API call after authentication which need Authorization in header.

###### Error
```
Error: Ember Data Request GET http://embertaskapi.test/api/tasks returned a 401
Payload (application/json)
[object Object]
at ErrorClass.AdapterError (/tmp/broccoli-9122c1h7IjFHtwVu/out-220-broccoli_merge_trees/assets/addon-tree-output/ember-data/-private.js:6175:1)
at new ErrorClass (/tmp/broccoli-9122c1h7IjFHtwVu/out-220-broccoli_merge_trees/assets/addon-tree-output/ember-data/-private.js:6203:1)
at Class.handleResponse (/tmp/broccoli-9122c1h7IjFHtwVu/out-220-broccoli_merge_trees/assets/addon-tree-output/ember-data/adapters/rest.js:801:1)
at ajaxError (/tmp/broccoli-9122c1h7IjFHtwVu/out-220-broccoli_merge_trees/assets/addon-tree-output/ember-data/adapters/rest.js:1093:1)
at ajaxErrorHandler (/tmp/broccoli-9122c1h7IjFHtwVu/out-220-broccoli_merge_trees/assets/addon-tree-output/ember-data/adapters/rest.js:1139:1)
at Object.hash.error (/tmp/broccoli-9122c1h7IjFHtwVu/out-220-broccoli_merge_trees/assets/addon-tree-output/ember-data/adapters/rest.js:884:1)
at fire (/var/www/html/hands-on-ember/node_modules/jquery-deferred/lib/jquery-callbacks.js:78:30)
at Object.fireWith (/var/www/html/hands-on-ember/node_modules/jquery-deferred/lib/jquery-callbacks.js:188:7)
at Object.fire [as reject] (/var/www/html/hands-on-ember/node_modules/jquery-deferred/lib/jquery-callbacks.js:195:10)
at onError (/var/www/html/hands-on-ember/node_modules/najax/lib/najax.js:208:9)
at dataHandler (/var/www/html/hands-on-ember/node_modules/najax/lib/najax.js:173:9)
at IncomingMessage. (/var/www/html/hands-on-ember/node_modules/najax/lib/najax.js:198:9)
at IncomingMessage.emit (events.js:194:15)
at endReadableNT (_stream_readable.js:1125:12)
at process._tickCallback (internal/process/next_tick.js:63:19)
```
It works fine without fastboot.

###### This is my `adapter.js`
```
import config from '../config/environment';
import DS from 'ember-data';
import { computed } from '@ember/object';
import { inject as service } from '@ember/service';
import { storageFor } from 'ember-local-storage';

export default DS.RESTAdapter.extend({
namespace: "api",
host: config.apiURL,
session: service('session'),
stats: storageFor('stats'),
headers: computed('stats.user', function () {
const user = this.get('stats.user');
// console.log('adpter', user);
return {
'Authorization': `Bearer ${user.access_token}`,
'Accept': 'application/json'
}
})
});

```

Your guidance will be highly appreciated and valuable to me.

Thanks,