code refactor Difficulty

Author: ibudisteanu

src/common/blockchain/global/difficulty/Blockchain-Difficulty.js

@@ -129,7 +129,7 @@ class BlockchainDifficulty{
 
         //avoid first Block, because the firstBlock is correlated with the last block of the POW
         const PoSModulo = BlockchainGenesis.PoSModulo(blockNumber);
-        if ( PoSModulo && (blockNumber+1) % PoSModulo === 10 ) firstBlock += 1
+        if ( PoSModulo && ( (blockNumber+1) % PoSModulo === 10 ) ) firstBlock += 1
 
         //adding blocks 0..8
         for (let i = firstBlock; i < blockNumber; i++) {