addPackageToProject(packageName, target) {
    let packageObject = { name: packageName };

    if (target) {
      packageObject.target = target;
    }

    return this.addPackagesToProject([packageObject]);
  }
Used to add a package to the project's `package.json`.

    Generally, this would be done from the `afterInstall` hook, to
    ensure that a package that is required by a given blueprint is
    available.

    @method addPackageToProject
    @param {String} packageName
    @param {String} target
    @return {Promise}