Satisfy rubocop

Gemfile.lock

 PATH
   remote: .
   specs:
-    gitlab-monitor (2.6.0)
+    gitlab-monitor (2.7.0)
       connection_pool (~> 2.2.1)
       pg (~> 0.18.4)
       quantile (~> 0.2.0)
@@ -25,7 +25,7 @@ GEM
     rack-protection (1.5.3)
       rack
     rainbow (2.1.0)
-    redis (3.3.3)
+    redis (3.3.5)
     redis-namespace (1.5.3)
       redis (~> 3.0, >= 3.0.4)
     rspec (3.5.0)
@@ -69,4 +69,4 @@ DEPENDENCIES
   rubocop (~> 0.42)
 
 BUNDLED WITH
-   1.13.2
+   1.16.1

lib/gitlab_monitor/database/row_count.rb

@@ -7,7 +7,7 @@ module GitLab
       # queries in the QUERIES constant. If in doubt how these work, read
       # #construct_query
       class RowCountCollector < Base
-        WHERE_MIRROR_ENABLED = <<~SQL
+        WHERE_MIRROR_ENABLED = <<~SQL.freeze
           projects.mirror = true
           AND project_mirror_data.retry_count <= 14
           AND (projects.visibility_level = 20 OR plans.name IN ('early_adopter', 'bronze', 'silver', 'gold'));
@@ -21,7 +21,7 @@ module GitLab
             LEFT JOIN plans ON namespaces.plan_id = plans.id
           SQL
           check: "SELECT 1 FROM information_schema.tables WHERE table_name='project_mirror_data'"
-        }
+        }.freeze
 
         QUERIES = {
           mirrors_ready_to_sync: MIRROR_QUERY.merge( # EE only