Add upper bound to nokogiri version (#3)

Author: xprazak2

openscap_parser.gemspec

@@ -36,7 +36,7 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
-  spec.add_dependency 'nokogiri'
+  spec.add_dependency "nokogiri", "~> 1.6"
   spec.add_development_dependency "bundler", "~> 2.0"
   spec.add_development_dependency "rake", "~> 10.0"
   spec.add_development_dependency "minitest", "~> 5.0"