Upgrade to GitHub-native Dependabot

[dependabot-preview]

Dependabot Preview will be shut down on August 3rd, 2021. In order to keep getting Dependabot updates, please merge this PR and migrate to GitHub-native Dependabot before then.

Dependabot has been fully integrated into GitHub, so you no longer have to install and manage a separate app. This pull request migrates your configuration from Dependabot.com to a config file, using the new syntax. When merged, 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, rather than the Dependabot dashboard, to monitor your version updates, and you'll configure Dependabot through the new config file rather than a UI.

If you've got any questions or feedback for us, please let us know by creating an issue in the dependabot/dependabot-core repository.

Learn more about migrating to GitHub-native Dependabot

Please note that regular @dependabot commands do not work on this pull request.

[codecov-commenter]

Codecov Report

Merging #456 (4bc5d57) into master (5feded4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #456   +/-   ##
=======================================
  Coverage   88.65%   88.65%           
=======================================
  Files           8        8           
  Lines         564      564           
=======================================
  Hits          500      500           
  Misses         64       64           

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