Screenshot URLs are not readable by the screenshots server

[danirabbit]

See: https://appstream.elementary.io/appcenter/html/bionic/main/issues/com.github.calo001.luna.html

These should instead be formatted like:

https://raw.githubusercontent.com/calo001/luna/master/data/images/screenshot_1.png

[calo001]

Thanks I had not realized that I used the url incorrectly, fixed, soon an update.