Fix appstream file validation
Created by: rffontenelle
$ /usr/bin/appstream-util validate data/io.github.cleomenezesjr.GetOverHere.appdata.xml.in
data/io.github.cleomenezesjr.GetOverHere.appdata.xml.in: FAILED:
• tag-missing : <content_rating> required [use https://odrs.gnome.org/oars]
• style-invalid : Not enough <screenshot> tags, minimum is 1
• tag-missing : <release> required
• tag-missing : <name> is not present
• tag-missing : <summary> is not present
• tag-missing : <url> is not present