Changes to skaffold.env don't trigger re-deploy

When running via `skaffold dev`, a change to `skaffold.yaml` will trigger a redeployment of the application without rebuilding the container.

A change to `skaffold.env` will be treated like any source file. If it's added to the container via a COPY, then a change will trigger a restart PLUS a Docker Build. Otherwise it's ignored, and changes don't trigger a redeployment.

Expected: `skaffold.env` should be watched by default, and changes to variable values should result in release deployments.