Update mongodb to version 2.2.21 🚀 (#3368)

* chore(package): update mongodb to version 2.2.20

https://greenkeeper.io/

* Fix race when fetching schema frequently

* Bumps mongo to 2.2.21

spec/ParseQuery.spec.js

@@ -1631,8 +1631,9 @@ describe('Parse.Query testing', () => {
       });
       expect(total).toBe(0);
       done()
-    }, () => {
+    }, (e) => {
       fail('should not fail');
+      fail(JSON.stringify(e));
       done();
     })
   });