Update package.json

missing devDependencies gulp-autoprefixer

packages/theme-chalk/package.json

@@ -28,7 +28,8 @@
   "devDependencies": {
     "gulp": "^3.9.1",
     "gulp-cssmin": "^0.1.7",
-    "gulp-sass": "^3.1.0"
+    "gulp-sass": "^3.1.0",
+    "gulp-autoprefixer": "^4.0.0"
   },
   "dependencies": {}
 }