ZCash pool fails to start, Field 'fOverwintered' not a field on NBitcoin.Transaction
Description

Starting ZCash, or any other pool with overwinter active.


Actual behavior
```
[2022-01-29 17:15:05.2875] [E] [zcash] Error during UpdateJob System.ArgumentException: Field 'fOverwintered' defined on type 'NBitcoin.Zcash.ZcashTransaction' is not a field on the target object which is of type 'NBitcoin.Transaction'.
   at System.Reflection.RtFieldInfo.SetValue(Object obj, Object value, BindingFlags invokeAttr, Binder binder, CultureInfo culture)
   at Miningcore.Blockchain.Equihash.EquihashJob.CreateOutputTransaction() in /home/ubuntu/test/miningcore/src/Miningcore/Blockchain/Equihash/EquihashJob.cs:line 79
   at Miningcore.Blockchain.Equihash.EquihashJob.BuildCoinbase() in /home/ubuntu/test/miningcore/src/Miningcore/Blockchain/Equihash/EquihashJob.cs:line 166
   at Miningcore.Blockchain.Equihash.EquihashJob.Init(EquihashBlockTemplate blockTemplate, String jobId, PoolConfig poolConfig, ClusterConfig clusterConfig, IMasterClock clock, IDestination poolAddressDestination, Network network, EquihashSolver solver) in /home/ubuntu/test/miningcore/src/Miningcore/Blockchain/Equihash/EquihashJob.cs:line 407
   at Miningcore.Blockchain.Equihash.EquihashJobManager.UpdateJob(CancellationToken ct, Boolean forceUpdate, String via, String json) in /home/ubuntu/test/miningcore/src/Miningcore/Blockchain/Equihash/EquihashJobManager.cs:line 126    at System.Reflection.RtFieldInfo.SetValue(Object obj, Object value, BindingFlags invokeAttr, Binder binder, CultureInfo culture)
   at Miningcore.Blockchain.Equihash.EquihashJob.CreateOutputTransaction() in /home/ubuntu/test/miningcore/src/Miningcore/Blockchain/Equihash/EquihashJob.cs:line 79
   at Miningcore.Blockchain.Equihash.EquihashJob.BuildCoinbase() in /home/ubuntu/test/miningcore/src/Miningcore/Blockchain/Equihash/EquihashJob.cs:line 166
   at Miningcore.Blockchain.Equihash.EquihashJob.Init(EquihashBlockTemplate blockTemplate, String jobId, PoolConfig poolConfig, ClusterConfig clusterConfig, IMasterClock clock, IDestination poolAddressDestination, Network network, EquihashSolver solver) in /home/ubuntu/test/miningcore/src/Miningcore/Blockchain/Equihash/EquihashJob.cs:line 407
   at Miningcore.Blockchain.Equihash.EquihashJobManager.UpdateJob(CancellationToken ct, Boolean forceUpdate, String via, String json) in /home/ubuntu/test/miningcore/src/Miningcore/Blockchain/Equihash/EquihashJobManager.cs:line 126
```


Keeps looping

Version
v68

Fresh pull without any changes. Using supplied coins.json and zcash_pool.json example file.