Bump rack from 2.0.8 to 2.1.1

Bumps [rack](https://github.com/rack/rack) from 2.0.8 to 2.1.1.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.0.8...2.1.1)

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

Gemfile

@@ -1,6 +1,6 @@
 source 'https://rubygems.org'
 
-gem 'rack', '~> 2.0' # ~> 2.0 requires ruby 2.2.2 or later.
+gem 'rack', '~> 2.1' # ~> 2.0 requires ruby 2.2.2 or later.
 gem 'hikidoc'
 gem 'fastimage'
 gem 'emot'

Gemfile.lock

@@ -64,7 +64,7 @@ GEM
       byebug (~> 11.0)
       pry (~> 0.10)
     public_suffix (3.1.1)
-    rack (2.0.8)
+    rack (2.1.1)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     racksh (1.0.0)
@@ -128,7 +128,7 @@ DEPENDENCIES
   octokit
   pit
   pry-byebug
-  rack (~> 2.0)
+  rack (~> 2.1)
   racksh
   rake
   redcarpet