Bump excon from 0.62.0 to 0.75.0 in /gpdb-doc/book

Bumps [excon](https://github.com/excon/excon) from 0.62.0 to 0.75.0.
- [Release notes](https://github.com/excon/excon/releases)
- [Changelog](https://github.com/excon/excon/blob/master/changelog.txt)
- [Commits](https://github.com/excon/excon/compare/v0.62.0...v0.75.0)
Signed-off-by: Ndependabot[bot] <support@github.com>

gpdb-doc/book/Gemfile.lock

@@ -65,7 +65,7 @@ GEM
       http_parser.rb (~> 0.6.0)
     erubis (2.7.0)
     eventmachine (1.2.7)
-    excon (0.62.0)
+    excon (0.75.0)
     execjs (2.7.0)
     faraday (0.15.4)
       multipart-post (>= 1.2, < 3)
@@ -152,11 +152,11 @@ 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)
+    nokogiri (1.10.9)
       mini_portile2 (~> 2.4.0)
     padrino-helpers (0.13.3.4)
       i18n (~> 0.6, >= 0.6.7)