Add bigdecimal to the development gemspec

Author: unixcharles

acme-client.gemspec

@@ -19,6 +19,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'rake', '~> 13.0'
   spec.add_development_dependency 'rspec', '~> 3.9'
   spec.add_development_dependency 'vcr', '~> 2.9'
+  spec.add_development_dependency 'bigdecimal'
   spec.add_development_dependency 'webmock', '~> 3.8'
   spec.add_development_dependency 'webrick', '~> 1.7'