Bump httparty version to remove transitive dependency on old, vulnerable json gem version

Author: fbacall

rdf-virtuoso.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |s|
   s.require_paths = ['lib']
 
   s.add_runtime_dependency 'rdf', '>= 3.1'
-  s.add_runtime_dependency 'httparty', '~> 0.12.0'
+  s.add_runtime_dependency 'httparty', '~> 0.18.1'
   s.add_runtime_dependency 'api_smith', '~> 1.3.0'
 
   s.add_development_dependency 'rspec', '~> 3.10'