Use ActiveRecord version instead of Rails'

...So this will work in non-Rails apps

lib/postgresql_cursor/active_record/connection_adapters/postgresql_type_map.rb

@@ -5,7 +5,7 @@ module ConnectionAdapters
       module PostgreSQLTypeMap
         # Returns the private "type_map" needed for the cursor operation
         def get_type_map # :nodoc:
-          if Rails::VERSION::MAJOR == 4 && Rails::VERSION::MINOR == 0
+          if ::ActiveRecord::VERSION::MAJOR == 4 && ::ActiveRecord::VERSION::MINOR == 0
             ::ActiveRecord::ConnectionAdapters::PostgreSQLAdapter::OID::TYPE_MAP
           else
             type_map