Fix tree invariants test (#1836)

Summary:
**Summary**

Disables auto-mocks on the tree data invariants test, thus fixing the Travis CI build.

**Test Plan**

```
npm test
```
Pull Request resolved: facebookarchive/draft-js#1836

Reviewed By: agoder

Differential Revision: D9301796

Pulled By: agoder

fbshipit-source-id: 879207e40da993eb4070d352ebc9535d7d23ad4e

Author: aforismesen

src/component/utils/exploration/__tests__/DraftTreeInvariants-test.js

@@ -13,6 +13,8 @@
 
 'use strict';
 
+jest.disableAutomock();
+
 // missing parent -> child connection
 
 const ContentBlockNode = require('ContentBlockNode');