gulpfile.js

(function() {

  'use strict';

  // Include Gulp & Plugins
  var gulp         = require('gulp'),
      sass         = require('gulp-sass'),
      cleanCSS     = require('gulp-clean-css'),
      autoprefixer = require('gulp-autoprefixer'),
      runSequence  = require('run-sequence'),
      concat       = require('gulp-concat'),
      rename       = require('gulp-rename'),
      uglify       = require('gulp-uglify'),
      jshint       = require('gulp-jshint'),
      plumber      = require('gulp-plumber'),
      gutil        = require('gulp-util');

  var onError = function( err ) {
    console.log('An error occurred:', gutil.colors.magenta(err.message));
    gutil.beep();
    this.emit('end');
  };

  // SASS
  gulp.task('sass', function () {
    return gulp.src('./assets/sass/*.scss')
    .pipe(plumber({ errorHandler: onError }))
    .pipe(sass())
    .pipe(autoprefixer())
    .pipe(rename({suffix: '.min'}))
    .pipe(cleanCSS())
    .pipe(gulp.dest('./assets/css'));
  });

  // JavaScript
  gulp.task('js', function() {
    return gulp.src([
      './bower_components/jquery/dist/jquery.js',
      './bower_components/jquery.fitvids/jquery.fitvids.js',
      './bower_components/jQuery-viewport-checker/dist/jquery.viewportchecker.min.js',
      './assets/js/script.js'])
      .pipe(jshint())
      .pipe(jshint.reporter('jshint-stylish'))
      .pipe(concat('app.js'))
      .pipe(rename({suffix: '.min'}))
      .pipe(uglify())
      .pipe(gulp.dest('./assets/js'));
  });

  // Watch
  gulp.task('watch', function() {
    gulp.watch('./assets/sass/**/*.scss', ['sass']);
    gulp.watch('./assets/js/**/*.js', ['js']);
  });

  // Build
  gulp.task('build', [], function() {
    runSequence('sass', 'js');
  });

  // Default
  gulp.task('default', ['watch'], function() {
    gulp.start('build');
  });

})();

Can you share your package.json? Thanks for this! So good!