Adding prepublishOnly script to package.json

package.json

@@ -9,7 +9,8 @@
   "scripts": {
     "start": "ts-node dependency-tree.ts",
     "build": "tsc",
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "test": "echo \"Error: no test specified\" && exit 1",
+    "prepublishOnly": "npm run build"
   },
   "author": "",
   "license": "ISC",