adding cluster_id index to cert_manager migrartion

db/migrate/20181101191341_create_clusters_applications_cert_manager.rb

@@ -7,10 +7,10 @@ class CreateClustersApplicationsCertManager < ActiveRecord::Migration
 
   def change
     create_table :clusters_applications_cert_managers do |t|
-      t.references :cluster, null: false, unique: true, foreign_key: { on_delete: :cascade }
+      t.references :cluster, null: false, unique: true, index: true, foreign_key: { on_delete: :cascade }
       t.integer :status, null: false
       t.string :version, null: false
-      t.string :email, null:false
+      t.string :email, null: false
       t.timestamps_with_timezone null: false
       t.text :status_reason
     end