Update notifications

targetconfig.json

@@ -31,7 +31,6 @@
         "zh-TW"
     ],
     "notifications": {
-        "pxt.microbit.org": "Hello world",
-        "localhost": "Testing"
+        "localhost": "<h2>Heads Up!</h2> <br />This editor is moving to <a href=\"https://makecode.microbit.org\" >https://makecode.microbit.org</a> on July 22nd 2017"
     }
 }