Special characters when uploading files

If a string contains special characters, it will not be sent when uploading files using the uploadFiles method. This is an error that only occurs on Android.
```
RNFS.uploadFiles({
toUrl: url,
files: files,
method: 'POST',
headers: {
'Accept': 'application/json',
},
fields: {
"foo": "éùà'ç"
}
})
```

I found this solution and it worked: [solution](https://github.com/itinance/react-native-fs/pull/1088)

Can the pull request be accepted?

It might help someone, so I'll leave it here anyway.

Maybe this other pull request will work as well, but I haven't tested it yet: [pull request](https://github.com/itinance/react-native-fs/pull/1045/files).