You do not have to move in a straight line.
Aggressive. As a bonus action, you can move up to your speed toward an enemy of your choice that you can see or hear. You must end this move closer to the enemy than you started.
Nothing about this feature indicates that you must move in a straight line. The only condition is that you must end up closer to the enemy than you started. You could actually move away for part of the movement or end up behind the enemy, as long as you are at least 1 square closer (if on a grid) than compared to where you started.
Some DMs might rule that you must move toward the enemy for every square of movement, but even this would not require a straight line (you could use diagonals). I interpret the meaning of moving toward the enemy as a constraint on the entire movement and not on every piece of the movement. The wording is a little ambiguous though, so there is room for differing opinion.