No longer able to provide nested path

I believe https://github.com/apache/cordova-plugin-file-transfer/pull/310 broke the previous behaviour. It was possible to provide a nested path as target file. Now it will throw an error when doing so.

## Code to reproduce
```
(() => {
const fileTransfer = new FileTransfer();
const url = 'http://cordova.apache.org/static/img/cordova_bot.png'
const filePath = window.cordova.file.dataDirectory + 'nested/test.png';

fileTransfer.download(
url,
filePath,
file => console.log(file),
error => console.error(error)
);
})()
```

## Possible fix
Adding this code snippet after [line 727](https://github.com/kpatfln/cordova-plugin-file-transfer/blob/2cdb0403a81821e144998c8d9a00d338d6ece3ee/src/android/FileTransfer.java#L727)
```
if(file == null){
file = new File(targetUri.getPath());
}
file.getParentFile().mkdirs();
```

Start in src/android/FileTransfer.java around line 727 and reproduce the download using the nested target path shown in the issue. Check the target-file handling and verify that downloading to nested/test.png creates the parent directories without throwing an error.

Written by the indexing model from the issue text.