ember-metrics Google Tag Manager not loading when you specify a data layer in the config

Hi @poteto

First of all, thanks for your addon, it looks really awesome!

I'm trying to track my app using GTM. I'm only on the first steps of my implementation, and I just did this into environment.js

ENV.metricsAdapters = [
    {
      name: 'GoogleTagManager',
      environments: ['development', 'production'],
      config: {
        id: 'GTM-NLXM2K',
        dataLayer: [{
          'pageCategory': 'signup',
          'visitorType': 'high-value'
        }]
      }
    }
  ];

And this in my router.js file

const Router = Ember.Router.extend({
  location: config.locationType,
  rootURL: config.rootURL,
  metrics: Ember.inject.service(),

  didTransition() {
    this._super(...arguments);
    this._trackPage();
  },

  _trackPage() {
    Ember.run.scheduleOnce('afterRender', this, () => {
      const page = this.get('url');
      const title = this.getWithDefault('currentRouteName', 'unknown');

      Ember.get(this, 'metrics').trackPage({ page, title });
    });
  }
});

Basically, nothing fancy, just your example from the Readme doc.

When doing so, I've got this error: 404: GET https://www.googletagmanager.com/gtm.js?id=GTM-NLXM2K&l=%5Bobject%20Object%5D

It's like it doesn't serialize the data layer.

Any clue how I can solve that? Also, I'm very keen to know how you can edit the datalayer on the fly depending on the route. Any example?

Thanks in advance