[release] 2.4.0

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "vuex",
-  "version": "2.3.1",
+  "version": "2.4.0",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {

package.json

@@ -1,6 +1,6 @@
 {
   "name": "vuex",
-  "version": "2.3.1",
+  "version": "2.4.0",
   "description": "state management for Vue.js",
   "main": "dist/vuex.common.js",
   "module": "dist/vuex.esm.js",