title: How can i use "of" in redux-observable
body: <p>I'm new to Redux-Observable. So, I apply redux-observable in my project, and i want to dispatch action by redux-observable so i used "of" (like Observable.of() in RXJS version before). But the reponse that i received is "Actions must be plain objects. Use custom middleware for async actions". Is there a wrong with my set up epic middleware or code? </p>
  
  <p><strong>store.js</strong></p>
  
  <pre><code>import { createStore, applyMiddleware, compose } from 'redux';
  import { createEpicMiddleware } from 'redux-observable';
  import { rootEpic } from './epics';
  import reducers from './reducers';
  
  const epicMiddleWare = createEpicMiddleware();
  const configureStore = () =&gt; {
    const store = createStore(
      reducers,
      compose(
        applyMiddleware(epicMiddleWare),
        window.devToolsExtension ? window.devToolsExtension() : (f) =&gt; { return f; },
      ),
    );
  
    epicMiddleWare.run(rootEpic);
  
    return store;
  };
  
  export default configureStore;
  </code></pre>
  
  <p><strong>epic.js</strong></p>
  
  <pre><code>export const fetchNavigationEpic = (action$) =&gt; {
    return action$
      .ofType(actionTypes.FETCH_NAVIGATION_LIST)
      .pipe(
        mergeMap(() =&gt; {
          return from(CreateService(SettingService).getAll())
            .pipe(
              map((response) =&gt; {
                if (response.status === 200) {
                  return of(fetchNavigationSuccess(response));
                }
  
                return fetchNavigationFailed(response);
              }),
            );
        }),
      );
  };
  </code></pre>
  
  <p><strong>action.js</strong></p>
  
  <pre><code>export const fetchNavigation = { type: actionTypes.FETCH_NAVIGATION_LIST };
  export const fetchNavigationSuccess = (payload) =&gt; {
    return { type: actionTypes.FETCH_NAVIGATION_LIST_SUCCESS, payload };
  };
  export const fetchNavigationFailed = (payload) =&gt; {
    return { type: actionTypes.FETCH_NAVIGATION_LIST_FAILED, payload };
  };
  </code></pre>
  
  <p>Library information:
   "redux-observable": "^1.0.0", 
   "rxjs": "^6.2.1",
   "rxjs-compat": "^6.2.1",</p>