Added missing [key] in beforeUpdate.

[psigen]

This adds a missing [key] reference to the beforeUpdate() hook that handles setting successfully updated file IDs. This matches the corresponding access in beforeInsert() on line 69 of the same file:
https://github.com/aldeed/meteor-cfs-autoform/blob/master/cfs-autoform-hooks.js#L69

This fixes an issue where uploading files using the cfs-files autoform type would lead to the following exception:

Exception in setTimeout callback: TypeError: CfsAutoForm.Util.deepFind(...).push is not a function
    at cb (http://localhost:3000/packages/cfs_autoform.js?0ada60c40a71ab26e12c4e697f33af05c95f1749:329:51)
    at null.<anonymous> (http://localhost:3000/packages/cfs_autoform.js?0ada60c40a71ab26e12c4e697f33af05c95f1749:382:13)
    at http://localhost:3000/packages/raix_eventemitter.js?9dbc8f21550d5b0e800bfa809850f28136f1deb6:131:16
    at Array.forEach (native)
    at Function._.each._.forEach (http://localhost:3000/packages/underscore.js?fa590de5090ceb4a42555b48562fd8f8e7035758:157:11)
    at _runCallbacks (http://localhost:3000/packages/raix_eventemitter.js?9dbc8f21550d5b0e800bfa809850f28136f1deb6:127:7)
    at EventEmitter.emit (http://localhost:3000/packages/raix_eventemitter.js?9dbc8f21550d5b0e800bfa809850f28136f1deb6:159:26)
    at oneChunkQueueEnded [as onEnded] (http://localhost:3000/packages/cfs_upload-http.js?40a85d8630caaae705a0a84cc6989fc98fda8487:511:19)
    at PowerQueue.next (http://localhost:3000/packages/cfs_power-queue.js?c62bc29a130805fdc29f80982e4cb5ebc5467dea:479:14)
    at http://localhost:3000/packages/cfs_power-queue.js?c62bc29a130805fdc29f80982e4cb5ebc5467dea:573:12