config(env) {
    let _env = env === undefined ? process.env.EMBER_ENV : env;
    let key = `${this.configPath()}|${_env}`;
    let config = this.configCache.get(key);
    if (config === undefined) {
      config = this.configWithoutCache(_env);
      this.configCache.set(key, config);
    }
    return cloneDeep(config);
  }
Loads the configuration for this project and its addons.

    @public
    @method config
    @param  {String} env Environment name
    @return {Object}     Merged configuration object