Bump rack from 2.0.6 to 2.0.8

Bumps [rack](https://github.com/rack/rack) from 2.0.6 to 2.0.8.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.0.6...2.0.8)

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

Author: dependabot[bot]

Gemfile.lock

@@ -12,7 +12,7 @@ GEM
     octokit (4.13.0)
       sawyer (~> 0.8.0, >= 0.5.3)
     public_suffix (3.0.3)
-    rack (2.0.6)
+    rack (2.0.8)
     rack-protection (2.0.4)
       rack
     sawyer (0.8.1)