Yarn merges `.yarnrc` from the current working directory with `.yarnrc` files
higher in the directory tree, so that file isn't needed in each package.
Unfortunately, npm doesn't do the same for `.npmrc` files, so a similar cleanup
isn't possible.
Add version info to `test_app/extensions/embark-service/package.json` to that
`yarn install` can work correctly if manually invoked in `test_app`.
Michael Bradley, Jr