Bump octokit from 4.12.0 to 4.13.0 in /docs

Bumps [octokit](https://github.com/octokit/octokit.rb) from 4.12.0 to 4.13.0.
- [Release notes](https://github.com/octokit/octokit.rb/releases)
- [Changelog](https://github.com/octokit/octokit.rb/blob/master/RELEASE.md)
- [Commits](https://github.com/octokit/octokit.rb/compare/v4.12.0...v4.13.0

)

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

docs/Gemfile.lock

@@ -217,7 +217,7 @@ GEM
     multipart-post (2.0.0)
     nokogiri (1.8.5)
       mini_portile2 (~> 2.3.0)
-    octokit (4.12.0)
+    octokit (4.13.0)
       sawyer (~> 0.8.0, >= 0.5.3)
     parallel (1.12.1)
     pathutil (0.16.1)