Fix extension for apply custom dataset which has jpg extension

[saintrealchoi]

Hello! First of all, Thank you for Awesome project.

I want to use your code on my images. but, when it has 'jpg' extension shell script do not recognize files. So, I fix it for all images which have other extension

Thank you!

[windj007]

Hi! Thank you for your contribution! Could you please change the default values to .png so the default behaviour is not changed after your fix?

[saintrealchoi]

Thank you for the review! I fix default values from .jpg to .png. :)