Update net-http-dependency to >= 4.0.1 and enable CI on Ruby 3.0.

Author: gkellogg

.github/workflows/ci.yml

@@ -24,7 +24,8 @@ jobs:
           - 2.5
           - 2.6
           - 2.7
-          #- ruby-head # Until net-http-persistent updated
+          - 3.0
+          - ruby-head
           - jruby
         gemfile:
           - Gemfile

sparql-client.gemspec

@@ -25,7 +25,7 @@ Gem::Specification.new do |gem|
   gem.required_ruby_version      = '>= 2.4'
   gem.requirements               = []
   gem.add_runtime_dependency     'rdf',       '~> 3.1'
-  gem.add_runtime_dependency     'net-http-persistent', '~> 4.0'
+  gem.add_runtime_dependency     'net-http-persistent', '~> 4.0', '>= 4.0.1'
   gem.add_development_dependency 'rdf-spec',  '~> 3.1'
   gem.add_development_dependency 'sparql',    '~> 3.1'
   gem.add_development_dependency 'rspec',     '~> 3.10'