Follow `.gitignore` on local build



Testing the config.yml with a local build takes a long a time (> 1 min.) on the “Checkout code” step as we have a Node.JS project with now >300MB node_modules. These are ignored in our Git repo, but it seems not in the local CircleCI build.
Therefore, I suggest to ignore what’s in .gitignore to speed up the local build. Related issue: How can ignore node_modules on local builds