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>

Gemfile

@@ -31,7 +31,7 @@ gem 'loog', '0.2.1'
 gem 'minitest', '5.11.3', require: false
 gem 'minitest-reporters', '1.3.6', require: false
 gem 'pgtk', '0.7.5'
-gem 'rack', '2.0.6'
+gem 'rack', '2.0.8'
 gem 'rack-ssl', '1.4.1'
 gem 'rack-test', '1.1.0'
 gem 'rake', '12.3.3', require: false

Gemfile.lock

@@ -98,7 +98,7 @@ GEM
       pg (~> 1.1)
       random-port (~> 0.3)
     powerpack (0.1.2)
-    rack (2.0.6)
+    rack (2.0.8)
     rack-protection (2.0.4)
       rack
     rack-ssl (1.4.1)
@@ -227,7 +227,7 @@ DEPENDENCIES
   minitest (= 5.11.3)
   minitest-reporters (= 1.3.6)
   pgtk (= 0.7.5)
-  rack (= 2.0.6)
+  rack (= 2.0.8)
   rack-ssl (= 1.4.1)
   rack-test (= 1.1.0)
   rake (= 12.3.3)