How to close testcafe runner

I'm using Testcafe runner to execute some tests i got. When everything is finished the console remains executing the script forever.

Here is my code:

createTestCafe('localhost', 1337, 1338)
.then(tc => {
    testcafe     = tc;
    runner = testcafe.createRunner();

    return runner
        .src(['offerRefresh.js'])
        .browsers(['nightmare'])
        .screenshots('./screenshots', true)
        .run();
})
.then(failedCount => {
    console.log('Tests failed: ' + failedCount);
    testcafe.close();
});

The console remains like this:

Tests failed: 0

And never closes the process.