can't use type=ArmorStand in minecraft 16w38a, is this a bug or an error on my part?
Entity savegame IDs have been modified for 1.11 to comply with the naming standard for other IDs (such as items and blocks). The IDs are now namespaced (defaulting to minecraft), are lowercase, and use underscores where there would be spaces. Some IDs have been completely renamed.
ArmorStand is now minecraft:armor_stand, or armor_stand:
/kill @e[type=armor_stand]
The wiki lists the new IDs here.