Merge pull request #927 from firebase/prameshj-patch-1

Upgrade to gulp-sass 5.0.0 to use node-sass 6.0.0

Author: prameshj

gulpfile.js

@@ -22,7 +22,7 @@ const fse = require('fs-extra');
 const flip = require('gulp-css-flip');
 const gulp = require('gulp');
 const path = require('path');
-const sass = require('gulp-sass');
+const sass = require('gulp-sass')(require('sass'));
 const streamqueue = require('streamqueue');
 const util = require('gulp-util');