create postReducer file and fix the reducer issue by implementing basic reducer code in index file of reducers

Author: vishalnagda1

src/reducers/index.js

@@ -0,0 +1,6 @@
+import { combineReducers } from 'redux';
+import postReducer from './postReducer';
+
+export default combineReducers({
+    posts: postReducer
+});