Relax dependencies to prep for 3.0 release.

Author: gkellogg

rdf-rdfxml.gemspec

@@ -22,22 +22,30 @@ Gem::Specification.new do |gem|
   gem.required_ruby_version = '>= 2.2.2'
   gem.requirements          = []
 
-  gem.add_runtime_dependency     'rdf',             '~> 2.0'
-  gem.add_runtime_dependency     'rdf-rdfa',        '~> 2.0'
-  gem.add_runtime_dependency     'rdf-xsd',         '~> 2.0'
+  #gem.add_runtime_dependency     'rdf',             '~> 3.0'
+  #gem.add_runtime_dependency     'rdf-rdfa',        '~> 3.0'
+  #gem.add_runtime_dependency     'rdf-xsd',         '~> 3.0'
+  gem.add_runtime_dependency     'rdf',             '>= 2.2', '< 4.0'
+  gem.add_runtime_dependency     'rdf-rdfa',        '>= 2.2', '< 4.0'
+  gem.add_runtime_dependency     'rdf-xsd',         '>= 2.2', '< 4.0'
   gem.add_runtime_dependency     'htmlentities',    '~> 4.3'
 
   #gem.add_development_dependency 'nokogiri' ,       '>= 1.6.1' # conditionally done in Gemfile
   #gem.add_development_dependency 'equivalent-xml' , '~> 0.2' # conditionally done in Gemfile
   gem.add_development_dependency 'open-uri-cached', '~> 0.0', '>= 0.0.5'
   gem.add_development_dependency 'spira',           '= 0.0.12'
-  gem.add_development_dependency 'json-ld',         '~> 2.0'
+  #gem.add_development_dependency 'json-ld',         '~> 3.0'
+  gem.add_development_dependency 'json-ld',         '>= 2.1', '< 4.0'
   gem.add_development_dependency 'rspec',           '~> 3.4'
   gem.add_development_dependency 'rspec-its',       '~> 1.2'
-  gem.add_development_dependency 'rdf-isomorphic',  '~> 2.0'
-  gem.add_development_dependency 'rdf-turtle',      '~> 2.0'
-  gem.add_development_dependency 'rdf-spec',        '~> 2.0'
-  gem.add_development_dependency 'rdf-vocab',       '~> 2.0'
+  #gem.add_development_dependency 'rdf-isomorphic',  '~> 3.0'
+  #gem.add_development_dependency 'rdf-turtle',      '~> 3.0'
+  #gem.add_development_dependency 'rdf-spec',        '~> 3.0'
+  #gem.add_development_dependency 'rdf-vocab',       '~> 3.0'
+  gem.add_development_dependency 'rdf-isomorphic',  '>= 2.2', '< 4.0'
+  gem.add_development_dependency 'rdf-turtle',      '>= 2.2', '< 4.0'
+  gem.add_development_dependency 'rdf-spec',        '>= 2.2', '< 4.0'
+  gem.add_development_dependency 'rdf-vocab',       '>= 2.2', '< 4.0'
   gem.add_development_dependency 'yard' ,           '~> 0.8'
 
   # Rubinius has it's own dependencies