minecraft-server: fix update script

Fixes 1.7.9 being newer than 1.7.10

pkgs/games/minecraft-servers/update.py

···
     Version object for 1.16.5.
     """
     return {
-        major_release: sorted(releases, key=lambda x: x.id, reverse=True)[0]
-        for major_release, releases in group_major_releases(releases).items()
+        major_release: max(
+            (release for release in releases if get_major_release(release.id) == major_release),
+            key=lambda x: tuple(map(int, x.id.split('.'))),
+        )
+        for major_release in group_major_releases(releases)
     }