Merge pull request #109 from acgotaku/greenkeeper/gulp-sass-4.0.0

Update gulp-sass to the latest version 🚀

package.json

@@ -46,7 +46,7 @@
     "gulp-imagemin": "^4.1.0",
     "gulp-plumber": "^1.1.0",
     "gulp-postcss": "^7.0.0",
-    "gulp-sass": "^3.1.0",
+    "gulp-sass": "^4.0.0",
     "gulp-sourcemaps": "^2.6.0",
     "gulp-stylelint": "^7.0.0",
     "gulp-tap": "^1.0.1",