docs(dart): tweak homepage banner

closes #1016

public/docs/dart/latest/_data.json

@@ -3,7 +3,7 @@
     "icon": "home",
     "title": "Angular Docs",
     "menuTitle": "Docs Home",
-    "banner": "Angular 2 is currently in Beta."
+    "banner": "Welcome to <b>angular.io/dart</b>! The current Angular 2 release is <b>beta.12</b>. See the <a href='https://github.com/angular/angular/blob/master/CHANGELOG.md' target='_blank'>Change Log</a> for recent enhancements, fixes, and breaking changes."
   },
 
   "quickstart": {
@@ -35,7 +35,7 @@
     "title": "API Preview",
     "reference": true
   },
-    
+
   "cheatsheet": {
     "title": "Angular Cheat Sheet",
     "intro": "A quick quide to Angular syntax.",
@@ -47,7 +47,7 @@
     "intro": "Brief definitions of the most important words in the Angular 2 vocabulary",
     "reference": true
   },
-  
+
   "resources": {
     "icon": "play-circle-fill",
     "title": "Angular Resources",
@@ -60,7 +60,7 @@
     "title": "Help & Support",
     "resources": true
   },
-  
+
   "styleguide": {
     "title": "Docs Style Guide",
     "intro": "Design & Layout Patterns For Documentation"