After trading at a premium since February, cybersecurity firm CrowdStrike Holdings (CRWD) will open down by around 6% today. The firm posted strong revenue growth, with annual recurring revenue topping $4.4 billion in the first quarter.CRWD stock is under pressure from the negative operating leverage. Its 19% top-line growth (on revenue of $1.1 billion) at a valuation of 25 times sales is excessive. The quarter also marks the first time since its IPO that the firm did not increase its quarter-on-quarter guidance.Discount retailer Dollar General (DG) gained 15.85% on Tuesday, adding to an…