Update dependencies.

Author: gkellogg

.travis.yml

@@ -1,12 +1,14 @@
 language: ruby
 bundler_args: --without debug
 script: "bundle exec rspec spec"
+before_install: "gem update --system"
 env:
   - CI=true
 rvm:
   - 2.2
   - 2.3
   - 2.4
+  - 2.5
   - jruby-9
   - rbx-3
 cache: bundler

README.md

@@ -31,8 +31,8 @@ Note that in most cases, if the instance is empty and mutable, the appropriate s
 
 ## Dependencies
 
-* [RDF.rb](http://rubygems.org/gems/rdf) (~> 2.0)
-* [RSpec](http://rubygems.org/gems/rspec) (~> 3.0)
+* [RDF.rb](http://rubygems.org/gems/rdf) (~> 3.0)
+* [RSpec](http://rubygems.org/gems/rspec) (~> 3.7)
 
 ## Installation
 

rdf-spec.gemspec

@@ -27,11 +27,10 @@ Gem::Specification.new do |gem|
   gem.required_ruby_version      = '>= 2.2.2'
   gem.requirements               = []
   gem.add_runtime_dependency     'rdf',             '~> 3.0'
-  #gem.add_runtime_dependency     'rdf-isomorphic',  '~> 3.0'
-  gem.add_runtime_dependency     'rdf-isomorphic',  '>= 2.0', '< 4.0'
+  gem.add_runtime_dependency     'rdf-isomorphic',  '~> 3.0'
   gem.add_runtime_dependency     'rspec',           '~> 3.7'
   gem.add_runtime_dependency     'rspec-its',       '~> 1.2'
-  gem.add_runtime_dependency     'webmock',         '~> 3.0'
+  gem.add_runtime_dependency     'webmock',         '~> 3.1'
   gem.add_development_dependency 'yard' ,           '~> 0.9.12'
   gem.post_install_message       = nil
 end