Build fix for boost 1.66
Build fix for boost 1.66

Stolen from here:
https://github.com/vergecurrency/VERGE/commit/a8ded5ca7c12c2080dc04443d1715ad4ac7f7b3b

MintcoinCommunity/Mintcoin-Desktop-Wallet,MintcoinCommunity/Mintcoin-Desktop-Wallet,MintcoinCommunity/Mintcoin-Desktop-Wallet,MintcoinCommunity/Mintcoin-Desktop-Wallet,MintcoinCommunity/Mintcoin-Desktop-Wallet,MintcoinCommunity/Mintcoin-Desktop-Wallet