run a build after npm install (#328)

Author: mwcz

package.json

@@ -8,7 +8,7 @@
     "build": "bash scripts/build.sh",
     "clean": "rm -rf node_modules package-lock.json {elements,themes}/*/{node_modules,package-lock.json}",
     "bootstrap": "lerna bootstrap --hoist",
-    "postinstall": "npm run bootstrap",
+    "postinstall": "npm run bootstrap && npm run build",
     "test-suite-inject": "node scripts/test-suite-inject.js",
     "doc-listing-inject": "node scripts/doc-listing-inject.js",
     "license-update": "node scripts/license-update.js",