[PR] Update types for WeakMap
[PR] Update types for WeakMap

Summary:
WeakMap doesn't currently accept Arrays as keys because Arrays are not subtypes of Objects in Flow's type system. This explicitly add support for Array keys to WeakMap.
Pull Request resolved: https://github.com/facebook/flow/pull/7262

Reviewed By: gabelevi

Differential Revision: D13602431

Pulled By: nmn

fbshipit-source-id: 2fb298d5a524c55760052e2d9ce2474f1f7795f7

nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow