gulpfile.js

var gulp        = require("gulp");
var sass        = require("gulp-sass");
var autoprefix  = require("gulp-autoprefixer");
var filter      = require('gulp-filter');
var browserSync = require('browser-sync');
var reload      = browserSync.reload;

/**
 * Start BrowserSync
 */
gulp.task('browser-sync', function () {
    browserSync({
        server: "./dist"
    });
});

/**
 * Compile sass
 */
gulp.task('sass', function () {
    return gulp.src('lib/scss/**/*.scss')
        .pipe(sass())
        .on('error', function(err){
            browserSync.notify(err.message, 3000);
            this.emit('end');
        })
        .pipe(autoprefix())
        .pipe(gulp.dest('lib/css'))
        .pipe(filter("**/*.css"))
        .pipe(reload({stream:true}));
});

/**
 * Watch
 */
gulp.task('default', ['sass', 'browser-sync'], function () {
    gulp.watch('lib/scss/**/*.scss', ['sass']);
});