Bump rack from 1.6.5 to 1.6.13 in /hooks/ruby/dismiss-review-server (github#315)

Bumps [rack](https://github.com/rack/rack) from 1.6.5 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@1.6.5...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]

hooks/ruby/dismiss-review-server/Gemfile.lock

@@ -10,7 +10,7 @@ GEM
       mime-types-data (~> 3.2015)
     mime-types-data (3.2016.0521)
     netrc (0.11.0)
-    rack (1.6.5)
+    rack (1.6.13)
     rack-protection (1.5.3)
       rack
     rest-client (2.0.1)