`pulumi update` failure when changing the events listened to

[ellismg]

I had a small hook deployment that was listening for the issues event and then modified my registration to listen for both issues and pull_request. The preview worked as expected, but doing the update caused this error:

Diagnostics:
  pulumi-nodejs:dynamic:Resource: new-issues-registration-pulumi
    error: Plan apply failed: {"message":"Validation Failed","errors":[{"resource":"Hook","code":"custom","message":"Hook already exists on this organization"}],"documentation_url":"https://developer.github.com/v3/orgs/hooks/#create-a-hook"}

I was able to work around this by destroying and then updating from scratch.