Apply Layout/LineLength rubocop rule

Note we're excluding a few files:

* Configuration files that weren't generated by us
* Migration files that weren't generated by us
* The Gemfile, since it includes an important comment that must be on
  the same line as the gem declaration
* The Budget::Stats class, since the heading statistics are a mess and
  having shorter lines would require a lot of refactoring

app/helpers/proposals_helper.rb

@@ -2,7 +2,8 @@ module ProposalsHelper
   def progress_bar_percentage(proposal)
     case proposal.cached_votes_up
     when 0 then 0
-    when 1..Proposal.votes_needed_for_success then (proposal.total_votes.to_f * 100 / Proposal.votes_needed_for_success).floor
+    when 1..Proposal.votes_needed_for_success
+      (proposal.total_votes.to_f * 100 / Proposal.votes_needed_for_success).floor
     else 100
     end
   end