chore: remove unused development dependency

Author: wincent

wikitext.gemspec

@@ -50,5 +50,4 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rake', '~> 13.0'
   s.add_development_dependency 'rspec', '~> 3.0'
   s.add_development_dependency 'yard', '~> 0.9'
-  s.add_development_dependency 'wopen3', '~> 0.3'
 end