Fix locking migration on statuses table. Nullable column and NO default value (#4825)

app/models/status.rb

@@ -22,7 +22,7 @@
 #  reblogs_count          :integer          default(0), not null
 #  language               :string
 #  conversation_id        :integer
-#  local                  :boolean          default(FALSE)
+#  local                  :boolean
 #
 
 class Status < ApplicationRecord

db/migrate/20170905165803_add_local_to_statuses.rb

@@ -1,5 +1,5 @@
 class AddLocalToStatuses < ActiveRecord::Migration[5.1]
   def change
-    add_column :statuses, :local, :boolean, null: true, default: false
+    add_column :statuses, :local, :boolean, null: true, default: nil
   end
 end

db/schema.rb

@@ -315,7 +315,7 @@ ActiveRecord::Schema.define(version: 20170905165803) do
     t.integer "reblogs_count", default: 0, null: false
     t.string "language"
     t.bigint "conversation_id"
-    t.boolean "local", default: false
+    t.boolean "local"
     t.index ["account_id", "id"], name: "index_statuses_on_account_id_id"
     t.index ["conversation_id"], name: "index_statuses_on_conversation_id"
     t.index ["in_reply_to_id"], name: "index_statuses_on_in_reply_to_id"