router.jsx: Remove unused state & replace parameter

The two arguments `state` and `replace` in `onEnter` are not required.
In the route when `/dashboard` matches, it is directed to `/` using
browserHistory.push().

Closes coala#137

src/router.jsx

@@ -27,7 +27,7 @@ import {parseRoute, buildRoute} from './route-utils';
 const routes = [
   // Redirect from `/dashboard` to `/`
   { path: '/dashboard',
-    onEnter: (state, replace) => history.push('/')
+    onEnter: () => history.push('/')
   },
   { path: '/',
     component: App,