Error prone GULP file

var runSequence = require('run-sequence');

var gulp = require('gulp'),
  less = require('gulp-less');
var rename = require('gulp-rename');
var autoprefixer = require('gulp-autoprefixer');
var minifycss = require('gulp-minify-css'),
  jshint = require('gulp-jshint'),
  stylish = require('jshint-stylish'),
  uglify = require('gulp-uglify'),
  usemin = require('gulp-usemin'),
  imagemin = require('gulp-imagemin'),
  rename = require('gulp-rename'),
  concat = require('gulp-concat'),
  notify = require('gulp-notify'),
  cache = require('gulp-cache'),
  changed = require('gulp-changed'),
  rev = require('gulp-rev'),
  del = require('del');
var browserSync = require('browser-sync').create();
var ngannotate = require('gulp-ng-annotate');
var watch = require('gulp-watch');



gulp.task('default', function() {
  // gulp.start('usemin', 'imagemin');
});



gulp.task('lessClean', function() {
  return del(['app/styles/yo.css']);
});


gulp.task('less', ['lessClean'], function() {
  return gulp.src('app/less/**/*.less')
    .pipe(less())
    .pipe(gulp.dest('app/styles'));
});

gulp.task('usemin', ['clean', 'less', 'jshint'], function() {
    return gulp.src('app/*.html')
    .pipe(usemin({
      css: [autoprefixer({
        browsers: ['last 2 versions'],
        cascade: false
      }), minifycss(), rev()],
      js: [ngannotate(), uglify(), rev()]
    }))
    .pipe(gulp.dest('dist/'));
});

gulp.task('jshint', function() {
  return gulp.src('app/scripts/**/*.js')
    .pipe(jshint())
    .pipe(jshint.reporter(stylish));
});


gulp.task('clean', function() {
  return del(['dist/**/*']);
});


//Watch task
gulp.task('watch', function() {
  // Watch .js files
  gulp.watch('{app/scripts/**/*.js,app/styles/**/*.css,app/**/*.html}', ['usemin', 'browser-sync']);
  // Watch image files
  gulp.watch('app/images/**/*', ['imagemin']);

  gulp.watch('dist/**/*', ['browser-sync']);
});


// Image minification task
gulp.task('imagemin', function() {
  return del(['dist/images']), gulp.src('app/images/**/*')
    .pipe(cache(imagemin({
      optimizationLevel: 3,
      progressive: true,
      interlaced: true
    })))
    .pipe(gulp.dest('dist/images'))
    .pipe(notify({
      message: 'Images task complete'
    }));
});


gulp.task('browser-sync', function() {
  var files = [
    'app/**/*.html',
    'app/styles/**/*.css',
    'app/images/**/*.png',
    'app/scripts/**/*.js',
    'dist/**/*'
  ];


  browserSync.init(files, {
    server: {
      baseDir: "dist",
      index: "index.html"
    }
  });

  // Watch any files in dist/, reload on change
  gulp.watch(['dist/**']).on('change', browserSync.reload);
});