Go back to @graph in frame usage.

Author: gkellogg

lib/frame.js

@@ -176,7 +176,7 @@ api.frame = (state, subjects, frame, parent, property = null) => {
     if(id in state.graphMap) {
       let recurse = false;
       let subframe = null;
-      if(!frame.hasOwnProperty('@graph')) {
+      if(!('@graph' in frame)) {
         recurse = state.graph !== '@merged';
         subframe = {};
       } else {