Fix the link of `global event bus` (#570)

Specify `v2` to the url, or the anchor will be removed because of the redirection.

docs/en/intro.md

@@ -58,6 +58,6 @@ This is the basic idea behind Vuex, inspired by [Flux](https://facebook.github.i
 
 Although Vuex helps us deal with shared state management, it also comes with the cost of more concepts and boilerplate. It's a trade-off between short term and long term productivity.
 
-If you've never built a large-scale SPA and jump right into Vuex, it may feel verbose and daunting. That's perfectly normal - if your app is simple, you will most likely be fine without Vuex. A simple [global event bus](http://vuejs.org/guide/components.html#Non-Parent-Child-Communication) may be all you need. But if you are building a medium-to-large-scale SPA, chances are you have run into situations that make you think about how to better handle state outside of your Vue components, and Vuex will be natural next step for you. There's a good quote from Dan Abramov, the author of Redux:
+If you've never built a large-scale SPA and jump right into Vuex, it may feel verbose and daunting. That's perfectly normal - if your app is simple, you will most likely be fine without Vuex. A simple [global event bus](http://vuejs.org/v2/guide/components.html#Non-Parent-Child-Communication) may be all you need. But if you are building a medium-to-large-scale SPA, chances are you have run into situations that make you think about how to better handle state outside of your Vue components, and Vuex will be natural next step for you. There's a good quote from Dan Abramov, the author of Redux:
 
 > Flux libraries are like glasses: you’ll know when you need them.