message: Add mapFields helper to the typings
  It allows to use the `mapFields` helper into the `Component` decorator:
  ```
  computed: {
  form: mapFields(),
  ...mapFields(['login', 'password']),
  ...mapFields({
  name: 'login',
  }),
  },
  })
  export default class Login extends Vue {
  ```
diff: @@ -175,6 +175,12 @@ export class ExtendOptions {
  paramNames?: string[];
  }
  +/**
  + * `mapFields` helper, which is similar to Vuex's `mapGetters` and `mapActions`
  + * as it maps a field object to a computed property.
  + */
  +export function mapFields(fields?: string[]|{[key: string]: string}): any;
  +
  export const version: string;
  export const install: Vue.PluginFunction<Configuration>
  