Bump rack from 2.2.17 to 2.2.18 in /examples/camping

Bumps [rack](https://github.com/rack/rack) from 2.2.17 to 2.2.18.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v2.2.17...v2.2.18)

---
updated-dependencies:
- dependency-name: rack
  dependency-version: 2.2.18
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

examples/camping/Gemfile

@@ -1,6 +1,6 @@
 source 'https://rubygems.org'
 
-gem 'rack', '~> 2.2.0'
+gem 'rack', '~> 2.2.18'
 gem 'rackup'
 gem 'camping', '< 3'
 gem 'markaby'

examples/camping/Gemfile.lock

@@ -24,7 +24,7 @@ GEM
     markaby (0.9.4)
       builder
     ostruct (0.6.2)
-    rack (2.2.17)
+    rack (2.2.18)
     rackup (1.0.1)
       rack (< 3)
       webrick
@@ -35,12 +35,13 @@ GEM
 
 PLATFORMS
   java
+  x86_64-linux
 
 DEPENDENCIES
   camping (< 3)
   jruby-jars (< 10)
   markaby
-  rack (~> 2.2.0)
+  rack (~> 2.2.18)
   rackup
   warbler!