Bump webrick from 1.7.0 to 1.8.1

Bumps [webrick](https://github.com/ruby/webrick) from 1.7.0 to 1.8.1.
- [Release notes](https://github.com/ruby/webrick/releases)
- [Commits](ruby/webrick@v1.7.0...v1.8.1)

---
updated-dependencies:
- dependency-name: webrick
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Gemfile

@@ -15,5 +15,5 @@ group :development, :test do
   gem 'eslintrb'
   gem 'test-unit'
   gem 'json-schema'
-  gem "webrick", "~> 1.7"
+  gem "webrick", "~> 1.8"
 end

Gemfile.lock

@@ -110,7 +110,7 @@ GEM
       ethon (>= 0.9.0)
     tzinfo (1.2.10)
       thread_safe (~> 0.1)
-    webrick (1.7.0)
+    webrick (1.8.1)
     yell (2.2.2)
 
 PLATFORMS
@@ -127,7 +127,7 @@ DEPENDENCIES
   kramdown-parser-gfm
   rake
   test-unit
-  webrick (~> 1.7)
+  webrick (~> 1.8)
 
 BUNDLED WITH
    2.2.3