Bring required state factory

It was removed from master in
2abbfad18c
but it's still required by the zone_specs and the address factory.

spec/factories/state_factory.rb

@@ -0,0 +1,13 @@
+FactoryBot.define do
+  factory :state, class: Spree::State do
+    name 'Alabama'
+    abbr 'AL'
+    country do |country|
+      if usa = Spree::Country.find_by_numcode(840)
+        country = usa
+      else
+        country.association(:country)
+      end
+    end
+  end
+end