Minecraft 1.8:
/setblock ~0 ~1 ~0 mob_spawner 0 replace {SpawnCount:1,SpawnRange:4,maxNearbyEntities:6,Delay:20,MinSpawnDelay:60,MaxSpawnDelay:120,EntityId:Zombie,SpawnData:{Equipment:[{},{id:leather_boots},{id:leather_leggings},{id:leather_chestplate},{id:leather_helmet}]}}
1.9
/setblock ~0 ~1 ~0 mob_spawner 0 replace {SpawnData:{ArmorItems:[{id:leather_boots},{id:leather_leggings},{id:leather_chestplate},{id:leather_helmet}],id:Zombie},SpawnCount:1,SpawnRange:4,maxNearbyEntities:6,Delay:20,MinSpawnDelay:60,MaxSpawnDelay:120}
Obs: Se precisar de mais alguma coisa no código é só avisar

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