docs(devguide): missed graphic and typos for dart setup

public/docs/dart/latest/guide/setup.jade

@@ -20,7 +20,7 @@
       dependencies:
         angular2: 2.0.0-alpha.20
         browser: any
-    
+
   p.
     The Dart Editor automatically downloads the packages your app depends on, along with any packages that they, in
     turn, depend on. If this download fails or you like using the command line, you can explicitly install packages.
@@ -30,7 +30,7 @@
 .l-main-section
   h2#section-create-an-entry-point Create an entry point
   p.
-    Create an <code>index.html</code> file and add the Angular library tags and a <code>main.js</code> file where
+    Create an <code>index.html</code> file and add the Angular library tags and a <code>main.dart</code> file where
     you'll build your first component.
 
   p.