var gulp = require('gulp'); 
var jshint = require('gulp-jshint');
var markdown = require('gulp-markdown');

gulp.task('default', function() {
  gulp.src('./*.js')
    .pipe(jshint())
    .pipe(jshint.reporter('default'))

  gulp.src('./*.md')
    .pipe(markdown())
    .pipe(gulp.dest('./build/markdown'));
});

gulp.task('watch', function() {
    gulp.watch('./*.js', ['default']);
    gulp.watch('./*.md', ['default']);
});

var gulp = require('gulp'); 
var jshint = require('gulp-jshint');
var markdown = require('gulp-markdown');

gulp.task('build', function () {
  gulp.src('./*.js')
    .pipe(jshint())
    .pipe(jshint.reporter('default'));
  gulp.src('./*.md')
    .pipe(markdown())
    .pipe(gulp.dest('./build/markdown'));
});

gulp.task('clean', function () {

})

gulp.task('watch', function () {
  gulp.watch('./*.js', ['default']);
  gulp.watch('./*.md', ['default']);
});

gulp.task('default', function (done) {
  gulp.series('clean', 'build', 'watch')
  done();
})

Update gulpfile.js