Add missing windows extensions

When running on Windows, wdm is required in order to properly do
incremental updates and regeneration.

The tzinfo-data dependency is also reported missing (under Windows
at least, with jekyll 3.9.3).

Gemfile

@@ -2,5 +2,7 @@
 
 source "https://rubygems.org"
 
+gem "wdm", "~> 0.1.1", :install_if => Gem.win_platform?
+
 gemspec
 

beautiful-jekyll-theme.gemspec

@@ -23,6 +23,8 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency "kramdown-parser-gfm", "~> 1.1"
   spec.add_runtime_dependency "kramdown", "~> 2.3"
   spec.add_runtime_dependency "webrick", "~> 1.8"
+  # This seems to only be required on Windows
+  spec.add_runtime_dependency "tzinfo-data", "~> 1.2023.3" if Gem.win_platform?
 
   spec.add_development_dependency "bundler", ">= 1.16"
   spec.add_development_dependency "rake", "~> 12.0"