t.end() gives false success on async tests

[sindresorhus]

This is kinda critical as it gives false success when you use t.end() in an async callback.

See: sindresorhus/is-online#17 (comment)

Example this makes the tests pass, even though it's should have failed:

test(function (t) {
    asyncFn(function (err, isAFalseValue) {
        t.assert(isAFalseValue);
        t.end();
    });
});

This works however:

test(function (t) {
    t.plan(1);

    asyncFn(function (err, isAFalseValue) {
        t.assert(isAFalseValue);
    });
});

[sindresorhus]

Added a test for this, which seems to pass, so might have been fixed after the really old currently published version.