Update documentation and version sync for 3.2.

Author: gkellogg

README.md

@@ -398,16 +398,16 @@ from BNode identity (i.e., they each entail the other)
 
 ## Dependencies
 
-* [Ruby](https://ruby-lang.org/) (>= 2.2)
+* [Ruby](https://ruby-lang.org/) (>= 2.6)
 * [LinkHeader][] (>= 0.0.8)
-* Soft dependency on [RestClient][] (>= 1.7)
+* Soft dependency on [RestClient][] (>= 2.1)
 
 ## Installation
 
 The recommended installation method is via [RubyGems](https://rubygems.org/).
 To install the latest official release of RDF.rb, do:
 
-    % [sudo] gem install rdf             # Ruby 2+
+    % [sudo] gem install rdf             # Ruby 2.6+
 
 ## Download
 

rdf.gemspec

@@ -31,7 +31,7 @@ Gem::Specification.new do |gem|
   gem.requirements               = []
   gem.add_runtime_dependency     'link_header', '~> 0.0', '>= 0.0.8'
   gem.add_runtime_dependency     'hamster',     '~> 3.0'
-  gem.add_development_dependency 'rdf-spec',    '~> 3.1'
+  gem.add_development_dependency 'rdf-spec',    '~> 3.2'
   gem.add_development_dependency 'rdf-turtle',  '~> 3.1'
   gem.add_development_dependency 'rdf-vocab',   '~> 3.1'
   gem.add_development_dependency 'rdf-xsd',     '~> 3.1'