fix: [torrust#226] user serde-bencode v0.2.4

There was a problem with list (nodes) containing other list (tuples)
with different value types.

```json
{
   "info": {
      "length": 8,
      "name": "minimal.txt",
      "piece length": 16384,
      "pieces": "<hex>30 9A 84 51 4A F1 09 D0 8C 34 42 11 26 67 7F 84 B3 23 4D 78</hex>"
   },
   "nodes": [
      [
         "188.163.121.224",
         56711
      ],
      [
         "162.250.131.26",
         13386
      ]
   ]
}
```