build(deps): bump rubyzip from 2.3.0 to 2.3.1 in /docs

Bumps [rubyzip](https://github.com/rubyzip/rubyzip) from 2.3.0 to 2.3.1.
- [Release notes](https://github.com/rubyzip/rubyzip/releases)
- [Changelog](https://github.com/rubyzip/rubyzip/blob/master/Changelog.md)
- [Commits](https://github.com/rubyzip/rubyzip/compare/v2.3.0...v2.3.1)

---
updated-dependencies:
- dependency-name: rubyzip
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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

docs/Gemfile.lock

@@ -251,7 +251,7 @@ GEM
     ruby-enum (0.9.0)
       i18n
     ruby2_keywords (0.0.4)
-    rubyzip (2.3.0)
+    rubyzip (2.3.1)
     safe_yaml (1.0.5)
     sass (3.7.4)
       sass-listen (~> 4.0.0)