Add and apply Style/BlockDelimiters rubocop rule

We were already using it most of the time, but there were a few places
were we used brackets for multiline blocks.

spec/controllers/comments_controller_spec.rb

@@ -3,9 +3,10 @@ require "rails_helper"
 describe CommentsController do
 
   describe "POST create" do
-
-    let(:legal_process) { create(:legislation_process, debate_start_date: Date.current - 3.days,
-                                                 debate_end_date: Date.current + 2.days) }
+    let(:legal_process) do
+      create(:legislation_process, debate_start_date: Date.current - 3.days,
+             debate_end_date: Date.current + 2.days)
+    end
     let(:question) { create(:legislation_question, process: legal_process, title: "Question 1") }
     let(:user) { create(:user, :level_two) }
     let(:unverified_user) { create(:user) }