Fix store state replacement

When replacing the store state with simple variable assignment,
the state object looses its observer and won't be reactive anymore.

Instead of replacing the whole state, each of the state's properties
should be replaced.

Source: vuejs/vuex#1118

Author: gryphon2411

src/auth/store.js

@@ -15,10 +15,14 @@ const auth = {
 
   mutations: {
     update (state, data) {
-      state = Object.assign({}, defaults, data)
+      Object.keys(state).forEach(index => {
+        state[index] = data[index]
+      })
     },
     clear (state) {
-      state = Object.assign(state, defaults)
+      Object.keys(state).forEach(index => {
+        state[index] = defaults[index]
+      })
     }
   },
 

src/store/common.js

@@ -54,7 +54,9 @@ export default {
     },
 
     clear (state) {
-      state = Object.assign({}, defaults)
+      Object.keys(state).forEach(index => {
+        state[index] = defaults[index]
+      })
     }
   },