Fix undefined parent in ParseRelation.add

Author: andrewimm

src/ParseRelation.js

@@ -82,7 +82,7 @@ export default class ParseRelation {
     var change = new RelationOp(objects, []);
     this.parent.set(this.key, change);
     this.targetClassName = change._targetClassName;
-    return parent;
+    return this.parent;
   }
 
   /**

src/__tests__/ParseRelation-test.js

@@ -86,7 +86,8 @@ describe('ParseRelation', () => {
     var r = new ParseRelation(parent, 'shipments');
     var o = new ParseObject('Delivery');
     o.id = 'D1';
-    r.add(o);
+    var p = r.add(o);
+    expect(p).toBeTruthy();
     expect(r.toJSON()).toEqual({
       __type: 'Relation',
       className: 'Delivery'