Add changelog, version information, frozen string literals

changelogs/unreleased/api-group-labels.yml

+---
+title: 'API: Add support for group labels'
+merge_request: 21368
+author: Robert Schilling
+type: added

lib/api/group_labels.rb

+# frozen_string_literal: true
+
 module API
   class GroupLabels < Grape::API
     include PaginationParams
@@ -9,6 +11,7 @@ module API
     end
     resource :groups, requirements: API::PROJECT_ENDPOINT_REQUIREMENTS do
       desc 'Get all labels of the group' do
+        detail 'This feature was added in GitLab 11.3'
         success Entities::Label
       end
       params do
@@ -21,6 +24,7 @@ module API
       end
 
       desc 'Create a new label' do
+        detail 'This feature was added in GitLab 11.3'
         success Entities::Label
       end
       params do
@@ -44,6 +48,7 @@ module API
       end
 
       desc 'Delete an existing label' do
+        detail 'This feature was added in GitLab 11.3'
         success Entities::Label
       end
       params do
@@ -59,6 +64,7 @@ module API
       end
 
       desc 'Update an existing label. At least one optional parameter is required.' do
+        detail 'This feature was added in GitLab 11.3'
         success Entities::Label
       end
       params do

spec/requests/api/group_labels_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe API::GroupLabels do