[bug] Image extension wrong for some thumbnails and covers

[ApexLiberta]

• Engine: [ex. Nodejs v12]
• I am using the latest version of this library (4.0.0)

Description
some images have mismatch extesnions

Code

in nhentai.net

<a href="/g/568442/1/">
  <img class="lazyload" width="350" height="487" data-src="//t4.nhentai.net/galleries/3317083/cover.jpg.webp" src="//t9.nhentai.net/galleries/3317083/cover.jpg.webp">
  <noscript><img src="//t4.nhentai.net/galleries/3317083/cover.jpg.webp" width="350" height="487"  /></noscript>
</a>

nlm.nhFetcher(568442).then((data) => {
	console.log("test", data);
});
// response 
{
    "raw": {
        "images": {
            "cover": {
                "t": "w",
                "w": 350,
                "h": 487
            },
            "thumbnail": {
                "t": "w",
                "w": 250,
                "h": 348
            }
        }
    },
    "id": 568442,
    "mediaId": 3317083,
    "titles": {
        "english": "[Joucho] Gal to Otaku no Idenshi Aishou Batsugun H",
        "japanese": "[情緒] ギャルとオタクの遺伝子相性抜群H",
        "pretty": "Gal to Otaku no Idenshi Aishou Batsugun H"
    },
    "url": "https://nhentai.net/g/568442",
    "cover": {
        "pageNumber": null,
        "extension": "webp",
        "height": 487,
        "width": 350,
        "url": "https://t.nhentai.net/galleries/3317083/cover.webp"
    },
    "thumbnail": {
        "pageNumber": null,
        "extension": "webp",
        "height": 348,
        "width": 250,
        "url": "https://t.nhentai.net/galleries/3317083/thumb.webp"
    }
}

Expected vs. Current behavior

https://t4.nhentai.net/galleries/3317083/cover.jpg.webp

should be the thumbnail or cover img link but in nhentai package it is

https://t.nhentai.net/galleries/3317083/thumb.webp

exapmle code 568442