Fix link (#276)

Author: mhienle

README.md

@@ -78,8 +78,7 @@ it is used by default in our
 
 ## Motivation
 
-Redux Thunk
-[middleware](https://github.com/reactjs/redux/blob/master/docs/advanced/Middleware.md)
+Redux Thunk [middleware](https://redux.js.org/advanced/middleware)
 allows you to write action creators that return a function instead of an action.
 The thunk can be used to delay the dispatch of an action, or to dispatch only if
 a certain condition is met. The inner function receives the store methods