Update webpack build cmd to production

Author: risenW

src/danfojs-browser/package.json

@@ -37,7 +37,7 @@
     "build:clean": "rimraf ./dist && rimraf ./lib && node ./scripts/prebuild.js && yarn run build",
     "dev": "nodemon",
     "lint": "eslint ./src",
-    "bundle": "webpack --mode development",
+    "bundle": "webpack --mode production",
     "coveralls": "cat ./coverage/lcov.info | ./node_modules/.bin/coveralls",
     "coverage": "nyc report --reporter=text-lcov | coveralls && nyc report --reporter=lcov",
     "patch": "npm version patch"