message: Make fetch optional at uiWorker
  Add warning messages when fetch or yoga don't passed.
diff: @@ -2,10 +2,27 @@ import { yogaWorker } from './workers/yogaWorker';
  import { base64ToBlobWorker } from './workers/base64ToBlobWorker';
  import { fetchWorker } from './workers/fetchWorker';
  -export const uiWorker = ({ yoga, fetch }) => event => {
  +interface TUIWorkerConfig {
  + yoga?: Object;
  + fetch?: (input: RequestInfo, init?: RequestInit) => Promise<Response>;
  +}
  +
  +export const uiWorker = (config: TUIWorkerConfig) => {
  + const { yoga, fetch } = config;
  + if (process.env.NODE_ENV !== 'production') {
  + if (typeof fetch !== 'function') {
  + console.warn("Fetch function don't passed to uiWorker: useFetch cannot work correctly");
  + }
  + if (typeof yoga !== 'object') {
  + console.warn("Yoga don't passed to uiWorker, auto-layout cannot work correctly");
  + }
  + }
  +
  + return event => {
  const message = event.data.pluginMessage;
  yogaWorker(yoga)(message);
  base64ToBlobWorker()(message);
  fetchWorker(fetch)(message);
  };
  +};
  