The best-selling Under Armour tee is on sale during Prime Day, and you can now grab the Under Armour Tech 2.0 short-sleeve T-shirt for just $13 at Amazon, which is almost 50% offThere are plenty of colors and sizing options to choose from, so you should be able to pick up a range of discounts depending on your choice.I own this T-shirt, and it's a staple summer workout top for me because it dries really quickly (I'm a sweaty exerciser, I won't l…