Bump plug_cowboy from 2.6.2 to 2.7.0 (#258)

Bumps [plug_cowboy](https://github.com/elixir-plug/plug_cowboy) from 2.6.2 to 2.7.0.
- [Changelog](https://github.com/elixir-plug/plug_cowboy/blob/master/CHANGELOG.md)
- [Commits](elixir-plug/plug_cowboy@v2.6.2...v2.7.0)

---
updated-dependencies:
- dependency-name: plug_cowboy
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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