replace pushd with cd

package.json

@@ -46,7 +46,7 @@
     "whatwg-fetch": "^0.11.0"
   },
   "scripts": {
-    "install": "pushd ./client; npm install; popd",
+    "postinstall": "cd ./client; npm install; cd ..",
     "build": "gulp build; webpack --progress --colors --config webpack.prd.config.js",
     "watch": "webpack --progress --colors --config webpack.dev.config.js & gulp watch",
     "start": "npm run watch",