Demo cannot handle input images of non 512x512 size

[MarcusW03]

I was running the demo of the mi-gan with my own set of testing images. I noticed that for images that aren't 512x512 an error is produced.
/scripts/demo.py", line 140, in main composed_img = img_resized * mask_resized + result_image * (1 - mask_resized) ~~~~~~~~~~~~^~~~~~~~~~~~~~ ValueError: operands could not be broadcast together with shapes (341,512,3) (340,512,1)

[MarcusW03]

The image that produced the above error has size of 1400x933

[MarcusW03]

Submitted Pull Request #18 for this issue.