docs: remove duplicated words in toh-pt6.jade

closes #1575

Author: twinssbc

public/docs/ts/latest/tutorial/toh-pt6.jade

@@ -235,7 +235,7 @@ code-example(format="." language="bash").
 :marked
   The same save method is used for both add and edit since `HeroService` will know when to call `post` vs `put` based on the state of the `Hero` object.
 
-  After we save a hero, we redirect the browser back to the to the previous page using the `goBack()` method.
+  After we save a hero, we redirect the browser back to the previous page using the `goBack()` method.
 
 +makeExample('toh-6/ts/app/hero-detail.component.ts', 'goback', 'app/hero-detail.component.ts (goBack)')(format=".")