Fix missing thumbnail in factorio publish package

Author: JanSharp

changelog.txt

@@ -1,5 +1,7 @@
 ---------------------------------------------------------------------------------------------------
 Version: 0.1.1
+  Changes:
+    - Fix missing thumbnail on mod portal
 ---------------------------------------------------------------------------------------------------
 Version: 0.1.0
 Date: 2021-10-25

scripts/publish.lua

@@ -279,6 +279,7 @@ if not args.skip_package then
     end)())
 
     root_filenames[#root_filenames+1] = "info.json"
+    root_filenames[#root_filenames+1] = "thumbnail.png"
     seven_zip("a", "-tzip", "-mx9", zip_path:str(), table.unpack(root_filenames))
 
     -- move all files in the zip archive into a `phobos` sub dir