Travis fails to deploy Cloudfoundry with buildpacks

Hello,
We are using Travis CI to build and deploy a NodeJS application to IBM Bluemix using the cloud foundry provider. It has been working fine until recently when we need to add a buildpack to the app. We added these to the manifest.yaml file,

buildpacks:
- https://github.com/johnwen84/bluemix-puppeteer-buildpack
- https://github.com/cloudfoundry/nodejs-buildpack

and now Travis fails on deployment with this error,
Waiting for API to complete processing files…
Job (f8cc92d4-a7f3-44eb-9719-48d551078624) failed: The app upload is invalid: Invalid zip archive.
FAILED
Logging out …

The reason why I think this might be related to Travis is that,

  1. The build/deployment goes successfully without the buildpack
  2. I can manually deploy the app successfully with the same manifest.yaml file, using the CF push command.

I’d really appreciate if someone can help me to figure out how to get around this problem.
Thanks
John