Allow for strings or json objects

src/notebook/notebook/nbformat.ts

@@ -88,8 +88,7 @@ namespace nbformat {
    */
   export
   interface MimeBundle extends JSONObject {
-    [key: string]: multilineString;
-    'application/json'?: any;
+    [key: string]: multilineString | JSONObject;
   }
   /* tslint:enable */
 

src/rendermime/index.ts

@@ -100,7 +100,7 @@ class RenderMime {
    * trusted (see [[preferredMimetype]]), and then pass a sanitizer to the
    * renderer if the output should be sanitized.
    */
-  render(options: RenderMime.IRenderOptions<string>): Widget {
+  render(options: RenderMime.IRenderOptions<string | JSONObject>): Widget {
     let { trusted, bundle, injector } = options;
     let mimetype = this.preferredMimetype(bundle, trusted);
     if (!mimetype) {