Relax required Nokogiri version (#117)

* Nokogiri 1.18.2 (Ruby >= 3.1)
* Nokogiri 1.17.x (Ruby >= 3.0)
* Nokogiri 1.16.8 (Ruby >= 3.1)
* Nokogiri 1.16.7 (Ruby >= 3.0)

Since strict version limitation was introduced via the following commit,

  Permit using nokogiri 1.11.0
  #54

but it seems no need to apply it.

Signed-off-by: Kentaro Hayashi <hayashi@clear-code.com>

Author: kenhys

fluent-plugin-winevtlog.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "bundler"
   spec.add_development_dependency "rake"
   spec.add_development_dependency "test-unit", "~> 3.4.0"
-  spec.add_development_dependency "nokogiri", [">= 1.10", "< 1.15"]
+  spec.add_development_dependency "nokogiri", "~> 1.10"
   spec.add_development_dependency "fluent-plugin-parser-winevt_xml", ">= 0.1.2"
   spec.add_runtime_dependency "fluentd", [">= 0.14.12", "< 2"]
   spec.add_runtime_dependency "win32-eventlog"