How to get gradle exec task to print std out in real-time

Question

I am executing a gradle exec task to build npm:

task build(type: Exec) {
    commandLine "npm","run", "build"
}

However, it only prints all of the standard output from npm run build when the task is completed. Whereas if you run it manually, it prints stuff to std out as it is running.

How do I get the std out to print in real-time?