Use version without patch in antora's config

Follow up to rubocop/rubocop@699e748.

docs/antora.yml

@@ -1,5 +1,7 @@
 name: rubocop-performance
 title: RuboCop Performance
+# We always provide version without patch here (e.g. 1.1),
+# as patch versions should not appear in the docs.
 version: master
 nav:
   - modules/ROOT/nav.adoc

tasks/cut_release.rake

@@ -41,11 +41,15 @@ namespace :cut_release do
     File.open('docs/antora.yml', 'w') do |f|
       f << antora_metadata.sub(
         'version: master',
-        "version: #{new_version}"
+        "version: #{version_sans_patch(new_version)}"
       )
     end
   end
 
+  def version_sans_patch(version)
+    version.split('.').take(2).join('.')
+  end
+
   def new_version_changes
     changelog = File.read('CHANGELOG.md')
     _, _, new_changes, _older_changes = changelog.split(/^## .*$/, 4)