function setPlanLimit(uint256 _planId, uint256 _perInvestorLimit, uint256 _addAmount) public onlyOwner {
        require(_planId >= 0 && _planId < investmentPlans_.length, "Wrong investment plan id");
        Objects.Plan storage plan = investmentPlans_[_planId];
        plan.perInvestorLimit = _perInvestorLimit;
        plan.leftAmount = plan.leftAmount.add(_addAmount);
        plan.lastUpdateDate = block.timestamp;
    }