“Fortnite” has become one of the biggest video game sensations in the world. Now its maker, Epic Games, is cashing in. Epic said last week it had raised $1.25 billion from a group that included investment firms like KKR, plus aXiomatic, the owner of the e-sports company Team Liquid. Behind the investment is the hope that “Fortnite” will remain a global phenomenon. Since it was released last year, teenagers and celebrities like Drake have hailed the game. It has made stars of prominent e-sports players like Tyler Blevins, who is known as Ninja.