MDL-77584 currencies: Fix outdated ISO 4217 code for Zambian Kwacha

On 2013-01-01 the ZMK code got replaced by the new ZMW code.

AMOS BEGIN
 MOV [ZMK,core_currencies],[ZMW,core_currencies]
AMOS END

lang/en/currencies.php

@@ -180,5 +180,5 @@
 $string['XPF'] = 'CFP Franc';
 $string['YER'] = 'Yemeni Rial';
 $string['ZAR'] = 'South African Rand';
-$string['ZMK'] = 'Zambian Kwacha';
+$string['ZMW'] = 'Zambian Kwacha';
 $string['ZWL'] = 'Zimbabwe Dollar';