Add and apply Rails/WhereNot rubocop rule

We simplify the code a little bit, and make it more consistent since we
were already using `where.not` in most places.

.rubocop.yml

@@ -325,6 +325,9 @@ Rails/UnknownEnv:
 Rails/Validation:
   Enabled: true
 
+Rails/WhereNot:
+  Enabled: true
+
 RSpec/AroundBlock:
   Enabled: true
 

app/models/debate.rb

@@ -45,7 +45,7 @@ class Debate < ApplicationRecord
   scope :sort_by_flags,            -> { order(flags_count: :desc, updated_at: :desc) }
   scope :sort_by_recommendations,  -> { order(cached_votes_total: :desc) }
   scope :last_week,                -> { where("created_at >= ?", 7.days.ago) }
-  scope :featured,                 -> { where("featured_at is not null") }
+  scope :featured,                 -> { where.not(featured_at: nil) }
   scope :public_for_api,           -> { all }
 
   # Ahoy setup
@@ -58,8 +58,7 @@ class Debate < ApplicationRecord
   end
 
   def self.recommendations(user)
-    tagged_with(user.interests, any: true)
-      .where("author_id != ?", user.id)
+    tagged_with(user.interests, any: true).where.not(author_id: user.id)
   end
 
   def searchable_translations_definitions

app/models/milestone.rb

@@ -15,7 +15,7 @@ class Milestone < ApplicationRecord
 
   scope :order_by_publication_date, -> { order(publication_date: :asc, created_at: :asc) }
   scope :published,                 -> { where("publication_date <= ?", Date.current.end_of_day) }
-  scope :with_status,               -> { where("status_id IS NOT NULL") }
+  scope :with_status,               -> { where.not(status_id: nil) }
 
   def self.title_max_length
     80

app/models/poll.rb

@@ -122,7 +122,7 @@ class Poll < ApplicationRecord
   end
 
   def self.not_voted_by(user)
-    where("polls.id not in (?)", poll_ids_voted_by(user))
+    where.not(id: poll_ids_voted_by(user))
   end
 
   def self.poll_ids_voted_by(user)

app/models/proposal.rb

@@ -106,7 +106,7 @@ class Proposal < ApplicationRecord
 
   def self.recommendations(user)
     tagged_with(user.interests, any: true)
-      .where("author_id != ?", user.id)
+      .where.not(author_id: user.id)
       .unsuccessful
       .not_followed_by_user(user)
       .not_archived

app/models/verification/management/managed_user.rb

@@ -2,7 +2,7 @@ class Verification::Management::ManagedUser
   include ActiveModel::Model
 
   def self.find(document_type, document_number)
-    User.where("document_number is not null").
+    User.where.not(document_number: nil).
     find_or_initialize_by(document_type:   document_type,
                           document_number: document_number)
   end

db/dev_seeds/flags.rb

@@ -1,19 +1,19 @@
 section "Flagging Debates & Comments" do
   40.times do
     debate = Debate.all.sample
-    flagger = User.where(["users.id <> ?", debate.author_id]).all.sample
+    flagger = User.where.not(id: debate.author_id).all.sample
     Flag.flag(flagger, debate)
   end
 
   40.times do
     comment = Comment.all.sample
-    flagger = User.where(["users.id <> ?", comment.user_id]).all.sample
+    flagger = User.where.not(id: comment.user_id).all.sample
     Flag.flag(flagger, comment)
   end
 
   40.times do
     proposal = Proposal.all.sample
-    flagger = User.where(["users.id <> ?", proposal.author_id]).all.sample
+    flagger = User.where.not(id: proposal.author_id).all.sample
     Flag.flag(flagger, proposal)
   end
 end