gulpfile.js

var gulp = require('gulp');
var shell = require('gulp-shell');
var browserSync = require('browser-sync').create();
var sass = require('gulp-sass');
var sourcemaps = require('gulp-sourcemaps');

// Task for building blog when something changed:
// gulp.task('build', shell.task(['bundle exec jekyll build --watch']));
// Or if you don't use bundle:
gulp.task('build', shell.task(['jekyll build --watch']));

// Task for serving blog with Browsersync
gulp.task('serve', function () {
    browserSync.init({server: {baseDir: '_site/'}});
    // Reloads page when some of the already built files changed:
    gulp.watch('_site/**/*.*').on('change', browserSync.reload);
});

gulp.task('sass', function () {
  return gulp.src('./_sass/main.scss')
    .pipe(sourcemaps.init())
    .pipe(sass().on('error', sass.logError))
    .pipe(sourcemaps.write())
    .pipe(gulp.dest('./_site/css'));
});

gulp.task('sass:watch', function () {
  gulp.watch('./_sass/*.scss', ['sass']);
});

gulp.task('default', ['build', 'sass', 'serve']);