docs(ngmodule): drop '_' in '_@NgModule' (#2217)

Author: wardbell

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

@@ -8,7 +8,7 @@ block includes
   **Angular Modules** help organize an application into cohesive blocks of functionality.
 
   An Angular Module is a _class_ adorned with the **@NgModule** decorator function.
-  `_@NgModule` takes a metadata object that tells Angular how to compile and run module code. 
+  `@NgModule` takes a metadata object that tells Angular how to compile and run module code. 
   It identifies the module's _own_ components, directives and pipes, 
   making some of them public so external components can use them. 
   It may add service providers to the application dependency injectors.