build web after install

package.json

@@ -91,11 +91,12 @@
   },
   "scripts": {
     "prepublish": "npm run buildweb",
+    "postinstall": "npm run buildweb",
     "test": "node test.js",
     "lint": "eslint .",
     "testserver": "node test/server/startServer.js",
     "testOutWeb": "jasmine test/spec_outweb/test_realweb_spec.js",
-    "buildweb": "NODE_ENV=production webpack --config web/webpack.config.js --colors",
+    "buildweb": "NODE_ENV=production npx webpack --config web/webpack.config.js --colors",
     "webserver": "NODE_ENV=test webpack --config web/webpack.config.js --colors --watch",
     "doc:serve": "node build_scripts/prebuild-doc.js && gitbook serve ./docs-src ./docs --log debug",
     "doc:build": "./build_scripts/build-doc-site.sh"