195fbfc784
Buildkit 0.13 introduced support for [multiple exporters](https://docs.docker.com/build/exporters/#multiple-exporters). We currently return an error in these situations. Instead, inspect the builder's version when loading the node and relax this error if we see it's running at least 0.13. Fixes https://github.com/pulumi/pulumi-docker-build/issues/21.