docs(router): fix Router.forRoot -> RouterModule.forRoot (#3172)

Author: mrkosima

public/docs/ts/latest/guide/router.jade

@@ -113,7 +113,7 @@ include ../../../_includes/_see-addr-bar
 a#example-config
 :marked
   The `appRoutes` array of *routes* describes how to navigate.
-  Pass it to the `Router.forRoot` method in the module `imports` to configure the router.
+  Pass it to the `RouterModule.forRoot` method in the module `imports` to configure the router.
 
   Each `Route` maps a URL `path` to a component.
   There are _no leading slashes_ in the _path_.