make sure devtool state travel work with strict mode

src/middlewares/devtool.js

@@ -8,9 +8,11 @@ export default {
     hook.emit('vuex:init', store)
     hook.on('vuex:travel-to-state', targetState => {
       const currentState = store._vm._data
+      store._dispatching = true
       Object.keys(targetState).forEach(key => {
         currentState[key] = targetState[key]
       })
+      store._dispatching = false
     })
   },
   onMutation (mutation, state) {