Bump puma from 4.3.3 to 4.3.9

Bumps [puma](https://github.com/puma/puma) from 4.3.3 to 4.3.9.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](https://github.com/puma/puma/compare/v4.3.3...v4.3.9)

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

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -57,7 +57,7 @@ GEM
     multipart-post (2.1.1)
     mustermann (1.1.1)
       ruby2_keywords (~> 0.0.1)
-    nio4r (2.5.2)
+    nio4r (2.5.8)
     nokogiri (1.10.9)
       mini_portile2 (~> 2.4.0)
     oauth2 (1.4.4)
@@ -70,7 +70,7 @@ GEM
       coderay (~> 1.1)
       method_source (~> 1.0)
     public_suffix (4.0.4)
-    puma (4.3.3)
+    puma (4.3.9)
       nio4r (~> 2.0)
     rack (2.2.2)
     rack-protection (2.0.8.1)