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

[mmphego]

Description

This PR fixes the issue experienced when downloading a new course. See screenshot below and issue referenced

Fixes # (issue)

This commit fixes #183

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

See #183

Configurations

OS: Ubuntu 20.04
Node version: v10.22.1
npm version: 6.14.6
Udacimak Version: v1.6.6
Browser: Brave(Chrome)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented on my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[jose0628]

Please merge this one! I have been waiting from months. Thanks