[PR] Fix type declaration for DedicatedWorkerGlobalScope.onmessage
[PR] Fix type declaration for DedicatedWorkerGlobalScope.onmessage

Summary:
It's just a two-character fix. :slightly_smiling_face:
Pull Request resolved: https://github.com/facebook/flow/pull/6853

Reviewed By: gabelevi

Differential Revision: D9754190

Pulled By: mrkev

fbshipit-source-id: 0496c3c89cec04416799299a61e8d6ebef982ea5

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