Add missing dependency in package.json

Author: woneob

package.json

@@ -23,9 +23,10 @@
     "gulp": "^3.9.0",
     "gulp-autoprefixer": "^3.1.0",
     "gulp-concat": "^2.6.0",
-    "gulp-minify-css": "^1.2.2",
     "gulp-header": "^1.7.1",
+    "gulp-minify-css": "^1.2.2",
     "gulp-rename": "^1.2.2",
+    "gulp-util": "^3.0.7",
     "run-sequence": "^1.1.5"
   },
   "spm": {