updated plugin to v1.1.0

v1.1.0 Changelog

New: added support for Woocommerce 2.1

New: only load the functions (tbz_add_my_currency &
tbz_add_my_currency_symbol) whcih add the Naira currency and symbol on
WordPress sites running Woocommerce version that are less that 2.1, as
it has been added to Woocommerce from version 2.1.

New: added verification checks to ensure the right amount is paid by the
customer

Fix: fixed Naira currency not displaying properly.

Fix: check if tbz_add_my_currency & tbz_add_my_currency_symbol functions
exist before declaring it.