Fixed incorrect call to init_mijireh()

WC_Gateway_Mijireh::init_mijireh() is now declared as "static", but it was called dynamically in WC_Gateway_Mijireh::process_payment(). Probably, it worked anyway due to PHP quirks, but I think it's better to make a clean call.
Merge pull request #1 from aelia-co/master

fixed incorrect call to init_mijireh()