This commit updates our CI setup to use local bin script instead of the
[npm module I found][module] to update the yarn.lock file on greenkeeper
package update PRs.
- While cross-origin PRs don't have access to project secrets,
installing and executing an external module in a step that has push
access to the repo on GitHub seemed risky
- yarn generate-lock-file does not fully resolve the modules and
confusingly generates a differently formatted yarn.lock file
[yarnpkg/yarn#2340][issue]
- Run a full yarn install so that a expected yarn.lock is
generated/updated
[issue]: https://github.com/yarnpkg/yarn/issues/2340
[module]:https://github.com/clarkbw/circleci-update-yarn-lock