remove usesInit condition (#824)

- rename: init -> beforeCreate in v2.0.0-alpha.7
- it's not necessary in the next version

src/mixin.js

@@ -2,8 +2,7 @@ export default function (Vue) {
   const version = Number(Vue.version.split('.')[0])
 
   if (version >= 2) {
-    const usesInit = Vue.config._lifecycleHooks.indexOf('init') > -1
-    Vue.mixin(usesInit ? { init: vuexInit } : { beforeCreate: vuexInit })
+    Vue.mixin({ beforeCreate: vuexInit })
   } else {
     // override init and inject vuex init procedure
     // for 1.x backwards compatibility.