Replace omnibus_updater with chef_client_updater

omnibus_updater is deprecated

cookbooks/chef_client_updater/libraries/matchers.rb

@@ -0,0 +1,7 @@
+if defined?(ChefSpec)
+  ChefSpec.define_matcher(:chef_client_updater)
+
+  def update_chef_client_updater(resource_name)
+    ChefSpec::Matchers::ResourceMatcher.new(:chef_client_updater, :update, resource_name)
+  end
+end