Remove useless command from build script

Author: PeachScript

package.json

@@ -13,7 +13,7 @@
   },
   "scripts": {
     "dev": "webpack-dev-server --inline --hot --quiet --port=8000",
-    "build": "rm -rf build/ && NODE_ENV=production webpack --progress --hide-modules",
+    "build": "NODE_ENV=production webpack --progress --hide-modules",
     "test": "karma start --single-run",
     "lint": "eslint './src/**(vue|js)'",
     "release": "bash ./release.sh"