Use `emitter.prependOnceListener(eventName, listener)`

[szmarczak]

See https://github.com/sindresorhus/got/issues/874

Just need to replace every .once with .prependOnceListener and do some basic test:

test('prepends once listener', t => {
    ...
    const timings = timer(request);
    request.once('response' => {
        t.true(typeof timings.response === 'number');
    });
    ...
});