Do not forget to the delete the PetBlocks.jar file on your server if you install the PetBlocks-Bukkit.jar file.
Use the PetBlocks-Bukkit.jar for Spigot, PaperSpigot and CraftBukkit.
Use the PetBlocks-Sponge.jar for Sponge.
The PetBlocks-Bukkit.jar is bigger as it supports more minecraft versions and different libraries.
Changes
Added support for Sponge (New features will still primary developed via Spigot, the support for Sponge is just another option)
Changed source code partially to Kotlin and because of the Kotlin libraries the PetBlocks.jar file gets bigger. The actual implementation stays as lightweight as it always has been.
Restructured source code because of sponge support