title: Write file RNFetchBlob overide files
body: <p>I'm using rnFetch blob to create files like:</p>
  
  <p>RNFetchBlob.fs.writeFile(uri, base64, "base64")</p>
  
  <p>It works but sometimes I need to override that image.</p>
  
  <p>As the <a href="https://github.com/joltup/rn-fetch-blob/wiki/File-System-Access-API#encodingutf8--base64--ascii--uri-1" rel="nofollow noreferrer">doc</a> says:</p>
  
  <p>writeFile API replaces content in the file, if you're going to append data to existing file[...]</p>
  
  <p>But it crashes the image and create a 0byte image when i try to overide using again.
  Anyone has passed by this?</p>