Add Docker and Travis config files to enable CI tests

Also fixes some Rails 6.0 deprecation warnings

app/models/bulk_update_request.rb

@@ -17,7 +17,7 @@ class BulkUpdateRequest < ApplicationRecord
   before_validation :normalize_text
   after_create :create_forum_topic
 
-  scope :pending_first, lambda { order("(case status when 'pending' then 0 when 'approved' then 1 else 2 end)") }
+  scope :pending_first, lambda { order(Arel.sql("(case status when 'pending' then 0 when 'approved' then 1 else 2 end)")) }
   scope :pending, ->{where(status: "pending")}
   scope :expired, ->{where("created_at < ?", TagRelationship::EXPIRY.days.ago)}
   scope :old, ->{where("created_at between ? and ?", TagRelationship::EXPIRY.days.ago, TagRelationship::EXPIRY_WARNING.days.ago)}

app/models/pool.rb

@@ -38,7 +38,7 @@ class Pool < ApplicationRecord
     end
 
     def series_first
-      order("(case pools.category when 'series' then 0 else 1 end), pools.name")
+      order(Arel.sql("(case pools.category when 'series' then 0 else 1 end), pools.name"))
     end
 
     def name_matches(name)

app/models/saved_search.rb

@@ -73,7 +73,7 @@ class SavedSearch < ApplicationRecord
 
   def self.labels_for(user_id)
     Cache.get(cache_key(user_id)) do
-      SavedSearch.where(user_id: user_id).order("label").pluck("distinct unnest(labels) as label")
+      SavedSearch.where(user_id: user_id).order("label").pluck(Arel.sql("distinct unnest(labels) as label"))
     end
   end
 

app/models/tag_relationship.rb

@@ -70,7 +70,7 @@ class TagRelationship < ApplicationRecord
     end
 
     def pending_first
-      order("(case status when 'pending' then 1 when 'queued' then 2 when 'active' then 3 else 0 end), antecedent_name, consequent_name")
+      order(Arel.sql("(case status when 'pending' then 1 when 'queued' then 2 when 'active' then 3 else 0 end), antecedent_name, consequent_name"))
     end
 
     def active