change github.com/mitchellh/mapstructure to github.com/go-viper/mapst… #3724

Job	Run time
Basic Checks	3m 0s
Unit Tests	14m 11s
Integration Tests (raft)	12m 49s
Integration Tests (pvtdata)	11m 45s
Integration Tests (pvtdatapurge e2e)	10m 59s
Integration Tests (ledger)	13m 6s
Integration Tests (lifecycle)	6m 4s
Integration Tests (smartbft)	19m 55s
Integration Tests (discovery gossip devmode pluggable)	6m 28s
Integration Tests (gateway idemix pkcs11 configtx configtxlator)	19m 20s
Integration Tests (sbe nwo msp)	8m 4s
	2h 5m 41s

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