Babel config: whitelist react.displayName
Babel config: whitelist react.displayName

Summary:
The react.displayName transform adds `displayName`s to React classes so
that the React devtools can show the component names.

Test Plan:
1. Make this change
2. Restart `make server`
3. Reload the page I was working on
4. Go to the react devtools tab
5. See component names again!

Auditors: kevinb, alpert

learningequality/perseus,ariabuckles/perseus,sachgits/perseus,abe4mvp/perseus,ariabuckles/perseus,ariabuckles/perseus,iamchenxin/perseus,alexristich/perseus,alexristich/perseus,ariabuckles/perseus,iamchenxin/perseus,abe4mvp/perseus,sachgits/perseus,learningequality/perseus