Bump puma from 3.10.0 to 4.3.8

Bumps [puma](https://github.com/puma/puma) from 3.10.0 to 4.3.8.
- [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/v3.10.0...v4.3.8)

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

Gemfile.lock

@@ -160,7 +160,9 @@ GEM
     mime-types (3.1)
       mime-types-data (~> 3.2015)
     mime-types-data (3.2016.0521)
-    mimemagic (0.3.2)
+    mimemagic (0.3.10)
+      nokogiri (~> 1)
+      rake
     mini_mime (0.1.4)
     mini_portile2 (2.3.0)
     minitest (5.11.3)
@@ -187,6 +189,7 @@ GEM
     multi_json (1.12.2)
     multipart-post (2.0.0)
     nested_form (0.3.2)
+    nio4r (2.5.2)
     nokogiri (1.8.5)
       mini_portile2 (~> 2.3.0)
     origin (2.3.1)
@@ -204,7 +207,8 @@ GEM
     pry-rails (0.3.6)
       pry (>= 0.10.4)
     public_suffix (3.0.0)
-    puma (3.10.0)
+    puma (4.3.8)
+      nio4r (~> 2.0)
     rack (1.6.10)
     rack-pjax (1.0.0)
       nokogiri (~> 1.5)