Wrong/missing translation for new spawn-eggs

The new spanweggs are missing a correct german translation.

Affected: Should be named as:
"Spawn Donkey" => "Erschaffe Esel"
"Spawn Mule" => "Erschaffe Maultier"
"Spawn Skeleton Horse" => "Erschaffe Skelett Pferd"
"Spawn Zombie Horse" => "Erschaffe Zombie Pferd"
"Spawn Polar Bear" => "Erschaffe Polarbär"