Bump rack from 2.0.7 to 2.0.8

Bumps [rack](https://github.com/rack/rack) from 2.0.7 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@2.0.7...2.0.8)

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

Author: dependabot[bot]

Gemfile.lock

@@ -148,7 +148,7 @@ GEM
     orm_adapter (0.5.0)
     public_suffix (4.0.1)
     puma (3.12.1)
-    rack (2.0.7)
+    rack (2.0.8)
     rack-pjax (1.1.0)
       nokogiri (~> 1.5)
       rack (>= 1.1)