filename ignored on android

**Describe the bug**

When specifying fileName its ignored on android and file saved under name inherited from URL. On iOS seem to be ok

**To Reproduce**

Just pass fileName prop to `enqueue`
```
await FlutterDownloader.enqueue(
url: url,
savedDir: saveDir.path,
fileName: "yourfilename.txt",
);
```

**Expected behavior**

I expect plugin to apply name specified name when downloading on android