Issue with the PUT request.

Nobody has claimed this yet.

I was testing this package, and I noticed that on a put request it doesn't overwrite the file the way I was expecting it to.

Test case was I posted a json file. Then I ran an update on that file will less content. It only replaced the amount of characters in the new file, but left the rest of the old file. Then I tested it with images, and though it displays the proper image, it still keeps the old bytes and size.

Example json post 1 => {"test1":"test1", "test2":"test2222222222222222222222"}
result => {"test1":"test1", "test2":"test2222222222222222222222"}

Example json post 2 => {"test1":"test1", "test2":"test2"}
result => {"test1":"test1", "test2":"test2"}2222222222222222222"}

Tested image size 1.3mb first. then uploaded a smaller image with the same name at 12kb. After uploading the file, the file size stayed the same, but showed the newer image.

I added this to the file_server.go and it fixed the issue. I was wondering if you could patch this and repush the image / repo?
Thanks in advance.

```
f.Truncate(0)
f.Seek(0, 0)

fsize, err := io.Copy(f, r.Body)
```

Start in file_server.go at the PUT file-writing path and reproduce the reported sequence with a longer JSON or image followed by a shorter replacement. Verify that the stored content and file size match the replacement completely, including the provided f.Truncate and f.Seek behavior.

Written by the indexing model from the issue text.