Update Dependabot config file (#1244)
Summary:
👋 Dependabot is moving natively into GitHub! This pull request updates your config file to the [new syntax](https://help.github.com/en/github/administering-a-repository/configuration-options-for-dependency-updates). When you merge this pull request, we'll swap out `dependabot-preview` (me) for a new `dependabot` app, and you'll be all set!
With this change, you'll now use the [Dependabot page in GitHub](https://github.com/facebook/flipper/network/updates), rather than the [Dependabot dashboard](https://app.dependabot.com/), to monitor your version updates. Dependabot is now configured exclusively using config files.
If you've got any questions or feedback for us, please let us know by creating an issue in the [dependabot/feedback](https://github.com/dependabot/feedback) repository.
[Learn more about the relaunch of Dependabot](https://github.blog/2020-06-01-keep-all-your-packages-up-to-date-with-dependabot/)
Please note that regular `dependabot` commands do not work on this pull request.
:robot:💛
Pull Request resolved: https://github.com/facebook/flipper/pull/1244
Reviewed By: nikoant
Differential Revision: D21998719
Pulled By: passy
fbshipit-source-id: 4e76f8a932d5c95e23a0445e8ed74f7b8fa28919
763853a7cf