added posts reducer

blog/src/reducers/index.js

@@ -1,7 +1,8 @@
 import { combineReducers } from 'redux';
+import PostsReducer from './reducer_posts';
 
 const rootReducer = combineReducers({
-  state: (state = {}) => state
+  posts: PostsReducer
 });
 
 export default rootReducer;

blog/src/reducers/reducer_posts.js

@@ -0,0 +1,11 @@
+import _ from 'lodash';
+import { FETCH_POSTS } from '../actions';
+
+export default function(state = {}, action) {
+  switch (action.type) {
+  case FETCH_POSTS:
+    return _.mapKeys(action.payload.data, 'id');
+  default:
+    return state;
+  }
+}