編集状態でのMarkdown preview追加

lib/reducer.js

@@ -109,6 +109,7 @@ function articles (state = initialArticles, action) {
 }
 
 function status (state = initialStatus, action) {
+  state = Object.assign({}, state)
   switch (action.type) {
     case SWITCH_FOLDER:
       state.mode = IDLE_MODE