We renamed the GitHub repository from `zeit/now` to `vercel/vercel` so this PR updates all references to the repo URL.
There were also a few remaining references to Now CLI that have been updated to Vercel CLI.
* Update links to `now-builders` repo to `now` repo
Also copies over the `.md` files from the now-builders' `errors`
directory so that the https://err.sh links work correctly.
Part of #2782.
* Update `err.sh` links that were formerly `now-cli`
* Empty commit for CI
* Make CircleCI `run.sh` script a bit better
Before it would fail with exit code 1 if there were no matching modified
files because of the `grep` call failing without any `packages` prefixed
files.
