Bump puma from 3.12.4 to 3.12.6

Bumps [puma](https://github.com/puma/puma) from 3.12.4 to 3.12.6.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](https://github.com/puma/puma/commits)

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

Author: dependabot[bot]

Gemfile.lock

@@ -95,7 +95,7 @@ GEM
     nokogiri (1.10.8)
       mini_portile2 (~> 2.4.0)
     public_suffix (3.0.3)
-    puma (3.12.4)
+    puma (3.12.6)
     rack (2.0.8)
     rack-proxy (0.6.5)
       rack