title: "Task never defined" error going from Gulp 3 to Gulp 4
body: <p>I'm trying to convert my gulp 3 file to gulp 4 after upgrading to Node v12, and I'm still erroring out even after reading tutorials/examples. I'm getting the <code>AssertionError [ERR_ASSERTION]: Task never defined: sass error</code></p>
  
  <p>My gulpfile.js file:</p>
  
  <pre><code>const gulp        = require('gulp');
  const browserSync = require('browser-sync').create();
  const sass        = require('gulp-sass');
  
  // Compile Sass &amp; Inject Into Browser
  gulp.task('sass', gulp.series('sass'), function() {
      return gulp.src(['node_modules/bootstrap/scss/bootstrap.scss', 'src/scss/*.scss'])
          .pipe(sass())
          .pipe(gulp.dest("src/css"))
          .pipe(browserSync.stream());
  });
  
  // Move JS Files to src/js
  gulp.task('js', gulp.series(['js']), function() {
      return gulp.src(['node_modules/bootstrap/dist/js/bootstrap.min.js', 'node_modules/jquery/dist/jquery.min.js','node_modules/popper.js/dist/umd/popper.min.js'])
          .pipe(gulp.dest("src/js"))
          .pipe(browserSync.stream());
  });
  
  // Watch Sass &amp; Serve
  gulp.task('serve', gulp.series(['sass']), function() {
  
      browserSync.init({
          server: "./src"  
      });
  
      gulp.watch(['node_modules/bootstrap/scss/bootstrap.scss', 'src/scss/*.scss'], gulp.series('sass'));
      gulp.watch("src/*.html").on('change', browserSync.reload);
  });
  
  // Move Fonts to src/fonts
  gulp.task('fonts', gulp.series(['fonts']), function() {
    return gulp.src('node_modules/font-awesome/fonts/*')
      .pipe(gulp.dest('src/fonts'))
  })
  
  // Move Font Awesome CSS to src/css
  gulp.task('fa', gulp.series(['fa']), function() {
    return gulp.src('node_modules/font-awesome/css/font-awesome.min.css')
      .pipe(gulp.dest('src/css'))
  })
  
  gulp.task('default', ['js','serve', 'fa', 'fonts']);
  </code></pre>
  
  <p>Any help is greatly appreciated, thanks!</p>