ERR: Cannot query field "part_keys" on type "Cohort"

**Describe the bug**
Issue when downloading a *beta* course.

**Screenshots**
![image](https://user-images.githubusercontent.com/7910856/104655824-f5a9ee80-56c6-11eb-864a-5150b20f0443.png)

**Desktop (please complete the following information):**
 - OS: Ubuntu 20.04
 - Node version: v10.22.1
 - npm version: 6.14.6
 - Udacimak Version: v1.6.6
 - Browser: Brave(Chrome)
