Fixes north america/US crosslinking stuff

lib/holidays.rb

@@ -259,6 +259,8 @@ private
 
     regions.flatten!
 
+    require "holidays/north_america" if regions.include?(:us) # special case for north_america/US cross-linking
+
     raise UnknownRegionError unless regions.all? { |r| r == :any or @@regions.include?(r) or begin require "holidays/#{r.to_s}"; rescue LoadError; false; end }
     regions
   end