docs: fix typo (#1021)

Author: Aaron Sum

Diff for: docs/guides/using-with-vuex.md

@@ -95,7 +95,7 @@ describe('Actions.vue', () => {
 
 What’s happening here? First we tell Vue to use Vuex with the `localVue.use` method. This is just a wrapper around `Vue.use`.
 
-We then make a mock store by calling `new Vuex.store` with our mock values. We only pass it the actions, since that’s all we care about.
+We then make a mock store by calling `new Vuex.Store` with our mock values. We only pass it the actions, since that’s all we care about.
 
 The actions are [jest mock functions](https://facebook.github.io/jest/docs/en/mock-functions.html). These mock functions give us methods to assert whether the actions were called or not.