bump dependencies and Jekyll version

Author: L. E. Segovia

.gitignore

@@ -2,4 +2,5 @@
 /*.gem
 Gemfile.lock
 dev_notes.md
-.vscode
+.vscode
+spec/fixtures/unit/.jekyll-cache

jekyll-target-blank.gemspec

@@ -17,8 +17,8 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
   spec.required_ruby_version = ">= 2.3.0"
 
-  spec.add_dependency "jekyll", "~> 3.0"
-  spec.add_dependency "nokogiri", "~> 1.8.2"
+  spec.add_dependency "jekyll", ">= 3.0", "<5.0"
+  spec.add_dependency "nokogiri", "~> 1.10"
 
   spec.add_development_dependency "bundler", "~> 1.6"
   spec.add_development_dependency "rake", "~> 12.0"