7.2 add preconditions to Shareable contructor
7.2 add preconditions to Shareable contructor

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