🔨 build: Upgrade build script.

Author: make-github-pseudonymous-again

package.json

@@ -65,7 +65,7 @@
     "url": "https://github.com/aureooms/js-red-black-tree"
   },
   "scripts": {
-    "build": "babel src -d lib",
+    "build": "rm -rf lib && babel src -d lib",
     "cover": "nyc --reporter=lcov npm test",
     "prepublish": "npm run build",
     "test": "ava",