Fixes a bug that caused miners to assume new epoch one block too early (#941)

Author: 1015bit

src/main/scala/io/iohk/ethereum/consensus/ethash/EthashMiner.scala

@@ -62,7 +62,7 @@ class EthashMiner(
           .getBlockForMining(blockValue)
           .map {
             case PendingBlockAndState(PendingBlock(block, _), _) => {
-              val blockNumber = block.header.number.toLong + 1
+              val blockNumber = block.header.number.toLong
               val epoch = EthashUtils.epoch(blockNumber, blockCreator.blockchainConfig.ecip1099BlockNumber.toLong)
               val (dag, dagSize) = calculateDagSize(blockNumber, epoch)
               val headerHash = crypto.kec256(BlockHeader.getEncodedWithoutNonce(block.header))