Fix issue with customFields not being inserted into createItem()

[ivarvermeulen]

I know this PR might be useless as the files I fixed should be generated from your API, but for me this was the only option to fix the issue. I've added the prepare script in the package.json in order to be able to install the package from my github fork, so running npm install https://github.com/The-Any-Thing/js-webflow-api as a temp fix

[dsinghvi]

👋 @ivarvermeulen We've just enabled stronger GitHub monitoring to track the issues. You'll see us being more responsive to these sorts of issues!

[travisjbeck]

man, i've been scratching my head trying to figure out why fieldData is typed like that in the API, how does anyone use this as is? Thanks.

[zplata]

Hey @ivarvermeulen @travisjbeck - we just shipped v2.4.0 which should allow extra data in fieldData to be set. Thank you @ivarvermeulen for contributions on this PR. As you've noticed, most of the SDK is automatically generated from our OpenAPI spec, so closing this for now, as it was addressed in the most recent release.