Support t.unique_constraint in db/schema.rb

[Kagemaru]

Currently, this entry in our db/schema.rb fails:

create_table "test", id: :serial, force: :cascade do |t|
  ...
  t.unique_constraint ["test"], name: "chk_unique_test"
end

With the following error message:

NoMethodError: undefined method `unique_constraint' for #<ActiveRecord::ConnectionAdapters::NullDBAdapter::TableDefinition:0x00007f7d96f662e0