Gulp: fix broken path in Sass

And when defining gulp-uglify-es needs '.default' at the end.

gulpfile.js

@@ -1,18 +1,18 @@
 var argv         = require('minimist')(process.argv.slice(2));
 var autoprefixer = require('gulp-autoprefixer');
+var cache        = require('gulp-cached');
 var chmod        = require('gulp-chmod');
 var concat       = require('gulp-concat');
 var git          = require('gulp-git');
 var gulp         = require('gulp');
 var gulpif       = require('gulp-if');
-var pug         = require('gulp-pug');
 var livereload   = require('gulp-livereload');
 var plumber      = require('gulp-plumber');
+var pug          = require('gulp-pug');
 var rename       = require('gulp-rename');
 var sass         = require('gulp-sass');
 var sourcemaps   = require('gulp-sourcemaps');
-var uglify       = require('gulp-uglify');
-var cache        = require('gulp-cached');
+var uglify       = require('gulp-uglify-es').default;
 
 var enabled = {
     uglify: argv.production,

src/styles/plugins/js_select2.sass

@@ -1,3 +1,6 @@
+@import ../../../node_modules/bootstrap/scss/functions
+@import ../../../node_modules/bootstrap/scss/variables
+@import ../../../node_modules/bootstrap/scss/mixins
 @import ../../../../pillar/src/styles/_config
 
 .select2-container

src/styles/plugins/pikaday.sass

@@ -1,3 +1,6 @@
+@import ../../../node_modules/bootstrap/scss/functions
+@import ../../../node_modules/bootstrap/scss/variables
+@import ../../../node_modules/bootstrap/scss/mixins
 @import ../../../../pillar/src/styles/_config
 @import ../../../../pillar/src/styles/_utils
 @charset "UTF-8"