Test for fake-timers was passing for the wrong reasons.

Nothing wrong with the implementation, but the test was only
checking test duration, not that the test passed. The test
was incorrecty using `t.end`, and so finished quicker than expected.

test/fixture/fake-timers.js

@@ -4,5 +4,4 @@ import sinon from 'sinon';
 test(t => {
 	sinon.useFakeTimers(Date.now() + 10000);
 	t.pass();
-	t.end();
 });

test/fork.js

@@ -70,6 +70,8 @@ test('fake timers do not break duration', function (t) {
 		.then(function (info) {
 			var duration = info.tests[0].duration;
 			t.true(duration < 1000, duration + ' < 1000');
+			t.is(info.stats.failCount, 0);
+			t.is(info.stats.passCount, 1);
 			t.end();
 		});
 });