Recommend using V4 API on chat slash command integrations

app/helpers/triggers_helper.rb

@@ -8,6 +8,6 @@ module TriggersHelper
   end
 
   def service_trigger_url(service)
-    "#{Settings.gitlab.url}/api/v3/projects/#{service.project_id}/services/#{service.to_param}/trigger"
+    "#{Settings.gitlab.url}/api/v4/projects/#{service.project_id}/services/#{service.to_param}/trigger"
   end
 end

spec/features/projects/services/mattermost_slash_command_spec.rb

@@ -159,7 +159,7 @@ feature 'Setup Mattermost slash commands', :feature, :js do
       it 'shows the correct trigger url' do
         value = find_field('request_url').value
 
-        expect(value).to match("api/v3/projects/#{project.id}/services/mattermost_slash_commands/trigger")
+        expect(value).to match("api/v4/projects/#{project.id}/services/mattermost_slash_commands/trigger")
       end
 
       it 'shows a token placeholder' do

spec/features/projects/services/slack_slash_command_spec.rb

@@ -40,6 +40,6 @@ feature 'Slack slash commands', feature: true do
 
   it 'shows the correct trigger url' do
     value = find_field('url').value
-    expect(value).to match("api/v3/projects/#{project.id}/services/slack_slash_commands/trigger")
+    expect(value).to match("api/v4/projects/#{project.id}/services/slack_slash_commands/trigger")
   end
 end