Fixes typo in Router tutorial (angular#2688)

Author: katerberg

public/docs/ts/latest/tutorial/toh-pt5.jade

@@ -576,7 +576,7 @@ block extract-id
 +makeExcerpt('app/hero-detail.component.html', 'back-button', '')
 
 :marked
-  Modifing the template to add this button spurs us to take one more
+  Modifying the template to add this button spurs us to take one more
   incremental improvement and migrate the template to its own file,
   called <span ngio-ex>hero-detail.component.html</span>: