Lambda PostDeployment never triggers

Hi,

I'm currently deploying the Identity project but I have an issue.

The PostDeployment Lambda is never triggered. Even after following Step 9 of the [documentation](https://github.com/awslabs/aws-amplify-identity-broker/blob/master/Documentation/UserDocumentation.md).

`amplify push --force` never triggers this lambda and I honestly never see where it should be triggered.