Bump puma from 3.12.0 to 4.3.5 in /gpdb-doc/book

Bumps [puma](https://github.com/puma/puma) from 3.12.0 to 4.3.5.
- [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: Ndependabot[bot] <support@github.com>

gpdb-doc/book/Gemfile.lock

@@ -152,11 +152,12 @@ GEM
     middleman-syntax (2.1.0)
       middleman-core (>= 3.2)
       rouge (~> 1.0)
-    mini_portile2 (2.3.0)
+    mini_portile2 (2.4.0)
     minitest (5.11.3)
     multi_json (1.13.1)
     multipart-post (2.0.0)
-    nokogiri (1.10.8)
+    nio4r (2.5.2)
+    nokogiri (1.10.9)
       mini_portile2 (~> 2.4.0)
     padrino-helpers (0.13.3.4)
       i18n (~> 0.6, >= 0.6.7)
@@ -166,7 +167,8 @@ GEM
       activesupport (>= 3.1)
     parallel (1.13.0)
     public_suffix (3.0.3)
-    puma (3.12.0)
+    puma (4.3.5)
+      nio4r (~> 2.0)
     rack (1.6.11)
     rack-livereload (0.3.17)
       rack