activeClassName docs update

Author: brandonlilly

docs/api/Link.md

@@ -22,7 +22,7 @@ State to persist to the `location`.
 
 #### `activeClassName`
 
-The className a `Link` receives when its route is active. Defaults to `active`.
+The className a `Link` receives when its route is active. No active class by default.
 
 #### `activeStyle`
 
@@ -55,4 +55,4 @@ Given a route like `<Route path="/users/:userId"/>`:
 
 // change style when link is active
 <Link to="/users" style={{color: 'white'}} activeStyle={{color: 'red'}}>Users</Link>
-```
+```