Change currency mnemonic for "New Israeli Shekel" from "ILS" to "NIS".

[Christian Stimming]

Log Message:
-----------
	Change currency mnemonic for "New Israeli Shekel" from "ILS" to
	"NIS". Fixes #152755.

Modified Files:
--------------
    gnucash:
        ChangeLog
    gnucash/src/engine:
        gnc-commodity.c
        iso-4217-currencies.scm