"clean" target removes package.json and leaves some files

[knok]

"make clean" command erases package.json and leaves the following files:
converters/snake1.png
converters/snake2.png
converters/snake2.sixel
test.log

It is not so important, but debian package system notices them.

[saitoha]

Thanks, Could you check fix-issue-7 branch?

[knok]

It works fine, thank you.