COMPASS-144 call stopPropagation() when cancel clicked (#565)

* COMPASS-144 call stopPropagation() when cancel clicked

otherwise the event bubbles up to the top and causes the page to reload, which takes the user back to the instance level.

* switch to preventDefault() because it’s less invasive.

Author: rueckstiess

src/auto-update/index.jade

@@ -1,6 +1,6 @@
 #auto-update
   .btn-group.pull-right
-    a.btn.btn-primary(data-hook='cancel') Not now
-    a.btn.btn-primary(data-hook='confirm') Yes please
-    
+    a.btn.btn-primary(data-hook='cancel', href='#') Not now
+    a.btn.btn-primary(data-hook='confirm', href='#') Yes please
+  
   p A newer version of Compass is now available! Would you like to install it and restart Compass?

src/auto-update/index.js

@@ -58,7 +58,8 @@ var NotificationUpdateAvailable = View.extend({
       }
     });
   },
-  cancel: function() {
+  cancel: function(evt) {
+    evt.preventDefault();
     this.visible = false;
     return false;
   },