Activating Feature Flags with Ember CLI

I was reading the documentation here, and it looks like I should be able to activate feature flags like this in my config/environment.js file:

var ENV = {
   EmberENV: {
      FEATURES: {
         'new-computed-syntax': true,
         'ember-htmlbars-component-generation': true
      }
   }
}

Yet this doesn't seem to be enough, even after restarting ember server. Any suggestions?