Generating GIF: Error: only integer scalar arrays can be converted to a scalar index

Current master raises this error when I execute this command:

```
$ python3 deepdreamer.py --gpuid 0 --gif true deepdreamer/demo1.jpg
...
Dream 97 saved.
Dream 98 saved.
Dream 99 saved.
Creating gif...
Error: only integer scalar arrays can be converted to a scalar index
```
The images are generated fine.