fix version warnings

Author: lorepirri

jekyll-theme-cayman-blog.gemspec

@@ -15,8 +15,8 @@ Gem::Specification.new do |s|
   end
 
   s.platform      = Gem::Platform::RUBY
-  s.add_runtime_dependency "jekyll", "~> 3.8.6"
-  s.add_runtime_dependency "jekyll-target-blank"
+  s.add_runtime_dependency "jekyll", '~> 3.8', '>= 3.8.6'
+  s.add_runtime_dependency "jekyll-target-blank", '>= 0'
   # s.add_runtime_dependency 'jekyll-seo-tag', '~> 2.0'
   s.add_development_dependency 'html-proofer', '~> 3.0'
   s.add_development_dependency 'rubocop', '~> 0.50'