fix(ngmodule): fix broken anchor (#2373)

Author: filipesilva

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

@@ -94,7 +94,7 @@ a#angular-modularity
 
   We'll see how later in the page. Let's start with the _root module_.
 
-a#root_module 
+a#root-module 
 .l-main-section
 :marked
   ## _AppModule_ - the application root module