Bump rack from 1.6.8 to 1.6.13 in /api/ruby/rendering-data-as-graphs (#311)

Bumps [rack](https://github.com/rack/rack) from 1.6.8 to 1.6.13.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@1.6.8...1.6.13)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

api/ruby/rendering-data-as-graphs/Gemfile.lock

@@ -18,7 +18,7 @@ GEM
     octokit (4.7.0)
       sawyer (~> 0.8.0, >= 0.5.3)
     public_suffix (3.0.0)
-    rack (1.6.8)
+    rack (1.6.13)
     rack-protection (1.5.3)
       rack
     sawyer (0.8.1)