SpringBoot Update default builder image for image builds with buildpacks

Now that the Cloud Native Buildpacks lifecycle supports multiple platform API versions Spring Boot can safely consume the latest Paketo builder image. This image will contain the latest lifecycle and will support API versions 0.3+. The platform API version can be configured by setting CNB_PLATFORM_API in the lifecycle container; it defaults to 0.3.

Also, the Paketo team is now recommending Dockerhub instead of GCR as the default location from which to pull images.

Comment From: scottfrederick

Thanks for the contribution @ekcasey!