Update Gemfile

Author: precondition

Gemfile

@@ -1,7 +1,8 @@
 source "https://rubygems.org"
 
-gem "jekyll", "~> 3.7.4"
-gem "github-pages", "~> 192"
-gem "rake", "~> 12.3.1"
-gem "slugify", "~> 1.0"
+gem "jekyll", "> 3.7.4"
+gem "github-pages", "> 193"
+gem "rake", "> 12.3.1"
+gem "slugify", "> 1.0"
 gem "jekyll-sitemap"
+gem "webrick" # https://stackoverflow.com/questions/65989040/bundle-exec-jekyll-serve-cannot-load-such-file