update wpsc-ru_RU.po

add missed
#: wpsc-components/theme-engine-v1/templates/wpsc-cart_widget.php:39
#: wpsc-theme/wpsc-cart_widget.php:39
msgid “Subtotal:”
msgstr “Итого:”

#: wpsc-components/theme-engine-v1/templates/wpsc-cart_widget.php:40
#: wpsc-theme/wpsc-cart_widget.php:40
msgid “excluding discount, shipping and tax”
msgstr “включая скидки, доставку и налоги”