Fix rubocop offenses

app/models/clusters/cluster.rb

@@ -6,7 +6,7 @@ module Clusters
 
     APPLICATIONS = {
       Clusters::Applications::Helm::NAME => Clusters::Applications::Helm
-    }
+    }.freeze
 
     belongs_to :user
 

app/models/clusters/platforms/kubernetes.rb

@@ -91,7 +91,7 @@ module Clusters
           api_url: api_url,
           namespace: namespace,
           token: token,
-          ca_pem: ca_cert,
+          ca_pem: ca_cert
         )
       end
 

db/migrate/20171031100710_create_clusters_kubernetes_helm_apps.rb

@@ -9,7 +9,7 @@ class CreateClustersKubernetesHelmApps < ActiveRecord::Migration
 
       t.datetime_with_timezone :created_at, null: false
       t.datetime_with_timezone :updated_at, null: false
-      
+
       t.integer :status, null: false
       t.string :version, null: false
       t.text :status_reason