Use PropTypes.array rather than invalid PropTypes.list
Use PropTypes.array rather than invalid PropTypes.list

Summary:
This avoids a console warning every time we use APINotLoaded.
There are no other uses of PropTypes.list in our code.

Test Plan: Manual

Reviewers: treaster

Reviewed By: treaster

Subscribers: changesbot

Projects: #changes_ui

Differential Revision: https://tails.corp.dropbox.com/D197409

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