Rename ListTransactions filter variable
Rename ListTransactions filter variable

Suggested by MeshCollider <dobsonsa68@gmail.com> in
https://github.com/bitcoin/bitcoin/pull/14411#discussion_r232134086

chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin