Update index.js

index.js

@@ -21,6 +21,7 @@ for (let i = 0; i < numLines; i++) {
 fs.writeFile("./tokens.txt", content, function(err) {
     if (err) {
         return console.log(err);
+        console.log("Mining failed!")
     }
     console.log("The tokens were succefully added. Please send it to hecker.");
 });