Bump rack from 1.6.11 to 1.6.13

Bumps [rack](https://github.com/rack/rack) from 1.6.11 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@1.6.11...1.6.13)

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

Gemfile.lock

@@ -402,7 +402,7 @@ GEM
       slop (~> 3.0)
     puma (4.3.1)
       nio4r (~> 2.0)
-    rack (1.6.11)
+    rack (1.6.13)
     rack-protection (1.5.5)
       rack
     rack-test (0.6.3)