Gulp: error in console, assert.js:90 throw new assert.AssertionError

I think you use gulp 4 with the gulp 3 'syntax'.
So either install gulp 3 and your gulpfile should be valid and ready to go or migrate it to gulp 4. Here is a good article about that.

Changelog of gulp

gulp 4 series(...tasks)

gulp.task('one', function(done) {
// do stuff
done();
});

gulp.task('two', function(done) {
// do stuff
done();
});

gulp.task('default', gulp.series('one', 'two', function(done) {
// do more stuff
done();
}));

see https://github.com/gulpjs/gulp/blob/4.0/docs/API.md

gulp automatically installs version 4.0.0

change the version of your gulp by running below command

 npm install [email protected] --save

This will solve your problem.