fixed multiple style guide violations

app/models/submission.rb

@@ -7,6 +7,8 @@ class Submission < ActiveRecord::Base
 
   belongs_to :exercise
 
+  delegate :execution_environment, to: :exercise
+
   scope :final, -> { where(cause: 'submit') }
   scope :intermediate, -> { where.not(cause: 'submit') }
 
@@ -24,10 +26,6 @@ class Submission < ActiveRecord::Base
     ancestors.merge(descendants).values
   end
 
-  def execution_environment
-    exercise.execution_environment
-  end
-
   [:download, :render, :run, :test].each do |action|
     filename = FILENAME_URL_PLACEHOLDER.gsub(/\W/, '')
     define_method("#{action}_url") do