Update bundle (with newest rubocop version) and fix offenses

db/migrate/20181129093207_drop_errors.rb

@@ -9,7 +9,6 @@ class DropErrors < ActiveRecord::Migration[5.2]
       scope :for_execution_environment, ->(execution_environment) { where(execution_environment_id: execution_environment.id) }
       scope :grouped_by_message, -> { select('MAX(created_at) AS created_at, MAX(id) AS id, message, COUNT(id) AS count').group(:message).order('count DESC') }
 
-      validates :execution_environment_id, presence: true
       validates :message, presence: true
 
       def self.nested_resource?