Update 0 Overview.md

moved the history declaration outside of the `render` function.

Author: Schniz

doc/00 Guides/0 Overview.md

@@ -138,10 +138,13 @@ var App = React.createClass({
   }
 });
 
+// Declare the history outside of the `render` function.
+var history = new HashHistory();
+
 // Finally we render a `Router` component with some `Route`s, it'll do all
 // the fancy routing stuff for us.
 React.render((
-  <Router history={new HashHistory}>
+  <Router history={history}>
     <Route path="/" component={App}>
       <Route path="about" component={About}/>
       <Route path="inbox" component={Inbox}/>
@@ -153,6 +156,7 @@ React.render((
 If you're not digging the JSX route config you can use plain objects:
 
 ```js
+var history = new HashHistory();
 var routes = {
   path: '/',
   component: App,
@@ -162,7 +166,7 @@ var routes = {
   ]
 };
 
-React.render(<Router history={new HashHistory} children={routes}/>, document.body);
+React.render(<Router history={history} children={routes}/>, document.body);
 ```
 
 Adding more UI
@@ -190,8 +194,9 @@ var Inbox = React.createClass({
   }
 });
 
+var history = new HashHistory();
 React.render((
-  <Router history={new HashHistory}>
+  <Router history={history}>
     <Route component={App}>
       <Route path="about" component={About}/>
       <Route path="inbox" component={Inbox}>