chore(docs): fix memory leak in example embed code

we need to sever the link between the main root scope and the example
root scope - this is only needed because we are embedding one app
in the other.

src/bootstrap/bootstrap-prettify.js

@@ -183,7 +183,9 @@ directive.ngEmbedApp = ['$templateCache', '$browser', '$rootScope', '$location',
   return {
     terminal: true,
     link: function(scope, element, attrs) {
-      var modules = [];
+      var modules = [],
+          embedRootScope,
+          deregisterEmbedRootScope;
 
       modules.push(['$provide', function($provide) {
         $provide.value('$templateCache', $templateCache);
@@ -209,10 +211,12 @@ directive.ngEmbedApp = ['$templateCache', '$browser', '$rootScope', '$location',
             }
           }, $delegate);
         }]);
-        $provide.decorator('$rootScope', ['$delegate', function(embedRootScope) {
-          docsRootScope.$watch(function embedRootScopeDigestWatch() {
+        $provide.decorator('$rootScope', ['$delegate', function($delegate) {
+          embedRootScope = $delegate;
+          deregisterEmbedRootScope = docsRootScope.$watch(function embedRootScopeDigestWatch() {
             embedRootScope.$digest();
           });
+
           return embedRootScope;
         }]);
       }]);
@@ -223,6 +227,12 @@ directive.ngEmbedApp = ['$templateCache', '$browser', '$rootScope', '$location',
           event.preventDefault();
         }
       });
+
+      element.bind('$destroy', function() {
+        deregisterEmbedRootScope();
+        embedRootScope.$destroy();
+      });
+
       angular.bootstrap(element, modules);
     }
   };