Bump puma from 4.3.8 to 4.3.9 (heroku#85)

Bumps [puma](https://github.com/puma/puma) from 4.3.8 to 4.3.9.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v4.3.8...v4.3.9)

---
updated-dependencies:
- dependency-name: puma
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Gemfile.lock

@@ -89,12 +89,12 @@ GEM
     minitest (5.11.3)
     msgpack (1.4.2)
     multi_json (1.13.1)
-    nio4r (2.5.7)
+    nio4r (2.5.8)
     nokogiri (1.12.5)
       mini_portile2 (~> 2.6.1)
       racc (~> 1.4)
     pg (0.21.0)
-    puma (4.3.8)
+    puma (4.3.9)
       nio4r (~> 2.0)
     racc (1.5.2)
     rack (2.2.3)