Update UsageWithReactRouter.md (#3459)

* Update UsageWithReactRouter.md

Without exact the All FilterLink will be always active

* Put the prop on its own line.

Author: ludovicoforace

docs/advanced/UsageWithReactRouter.md

@@ -144,6 +144,7 @@ import { NavLink } from 'react-router-dom'
 
 const FilterLink = ({ filter, children }) => (
   <NavLink
+    exact
     to={filter === 'SHOW_ALL' ? '/' : `/${filter}`}
     activeStyle={{
       textDecoration: 'none',