change Math to a library instead of a contract
change Math to a library instead of a contract

OpenZeppelin/openzeppelin-contracts,pash7ka/zeppelin-solidity,OpenZeppelin/openzeppelin-contracts,pash7ka/zeppelin-solidity,dmx374/zeppelin-solidity,OpenZeppelin/zeppelin-solidity,OpenZeppelin/zep-solidity,OpenZeppelin/zep-solidity,OpenZeppelin/openzeppelin-contracts,OpenZeppelin/zeppelin-solidity,dmx374/zeppelin-solidity